From 1122de18a55b5428c31157f9d841d2e44d8dfd1c Mon Sep 17 00:00:00 2001
From: Steven Hugg <hugg@fasterlight.com>
Date: Sat, 15 Aug 2026 12:03:22 +0200
Subject: [PATCH] added some more unit tests

---
 test/unit/testbaseplatform.ts | 660 ++++++++++++++++++++++++++++++++++
 test/unit/testcommon.ts       | 256 +++++++++++++
 test/unit/testcommon_ext.ts   | 361 +++++++++++++++++++
 test/unit/testemu.ts          | 522 +++++++++++++++++++++++++++
 4 files changed, 1799 insertions(+)
 create mode 100644 test/unit/testbaseplatform.ts
 create mode 100644 test/unit/testcommon.ts
 create mode 100644 test/unit/testcommon_ext.ts
 create mode 100644 test/unit/testemu.ts

diff --git a/test/unit/testbaseplatform.ts b/test/unit/testbaseplatform.ts
new file mode 100644
index 00000000..cf12ac45
--- /dev/null
+++ b/test/unit/testbaseplatform.ts
@@ -0,0 +1,660 @@
+
+import assert from "assert";
+import { describe, it } from "mocha";
+import {
+  DebugSymbols,
+  isDebuggable,
+  Debuggable,
+  BreakpointList,
+  BasePlatform,
+  BaseDebugPlatform,
+  Base6502Platform,
+  BaseZ80Platform,
+  Base6809Platform,
+  EmuState,
+  CpuState,
+  OpcodeMetadata,
+  Platform,
+  getToolForFilename_6502,
+  getToolForFilename_z80,
+  getToolForFilename_6809,
+  getOpcodeMetadata_6502,
+  cpuStateToLongString_6502,
+  cpuStateToLongString_Z80,
+  cpuStateToLongString_6809,
+  inspectSymbol,
+  lookupSymbol,
+  dumpStackToString,
+} from "../../src/common/baseplatform";
+
+describe('DebugSymbols', function () {
+  it('should create symbol map with correct structure', function () {
+    const symbolmap = { main: 0x0000, loop: 0x0010, end: 0x0100 };
+    const debuginfo = { platform: 'test' };
+    const symbols = new DebugSymbols(symbolmap, debuginfo);
+
+    assert.strictEqual(symbols.symbolmap['main'], 0x0000);
+    assert.strictEqual(symbols.symbolmap['loop'], 0x0010);
+    assert.strictEqual(symbols.symbolmap['end'], 0x0100);
+  });
+
+  it('should create inverted address-to-symbol map', function () {
+    const symbolmap = { main: 0x0000, loop: 0x0010, end: 0x0100 };
+    const debuginfo = {};
+    const symbols = new DebugSymbols(symbolmap, debuginfo);
+
+    assert.strictEqual(symbols.addr2symbol[0x0000], 'main');
+    assert.strictEqual(symbols.addr2symbol[0x0010], 'loop');
+    assert.strictEqual(symbols.addr2symbol[0x0100], 'end');
+  });
+
+  it('should ensure sentinel values in address map', function () {
+    const symbolmap = { loop: 0x1000 };
+    const debuginfo = {};
+    const symbols = new DebugSymbols(symbolmap, debuginfo);
+
+    // Empty symbol map gets $00 sentinel
+    assert.strictEqual(symbols.addr2symbol[0x0], '$00');
+    assert.strictEqual(symbols.addr2symbol[0x10000], '__END__');
+  });
+
+  it('should store debug info', function () {
+    const debuginfo = { platform: 'c64', version: '1.0' };
+    const symbols = new DebugSymbols({}, debuginfo);
+
+    assert.deepStrictEqual(symbols.debuginfo, debuginfo);
+  });
+
+  it('should handle empty symbol map', function () {
+    const symbols = new DebugSymbols({}, {});
+
+    assert.deepStrictEqual(symbols.symbolmap, {});
+    assert.ok(symbols.addr2symbol[0x0] !== undefined);
+  });
+
+  it('should handle duplicate addresses with last symbol winning', function () {
+    const symbolmap = { sym1: 0x100, sym2: 0x100 };
+    const symbols = new DebugSymbols(symbolmap, {});
+
+    // One of them should be in the inverted map
+    assert.ok(symbols.addr2symbol[0x100] === 'sym1' || symbols.addr2symbol[0x100] === 'sym2');
+  });
+});
+
+describe('isDebuggable type guard', function () {
+  it('should identify debuggable objects', function () {
+    const debuggable: Debuggable = {
+      getDebugCategories: () => ['CPU', 'Memory'],
+      getDebugInfo: (category: string) => 'debug info'
+    };
+
+    assert.ok(isDebuggable(debuggable));
+  });
+
+  it('should reject non-debuggable objects', function () {
+    assert.ok(!isDebuggable({}));
+    assert.ok(!isDebuggable(null));
+    assert.ok(!isDebuggable(undefined));
+    assert.ok(!isDebuggable({ foo: 'bar' }));
+  });
+
+  it('should accept partial implementations', function () {
+    const partial = {
+      getDebugCategories: () => ['CPU']
+    };
+
+    assert.ok(isDebuggable(partial));
+  });
+});
+
+describe('BreakpointList', function () {
+  it('should return null when no breakpoints exist', function () {
+    const list = new BreakpointList();
+    const cond = list.getDebugCondition();
+
+    assert.strictEqual(cond, null);
+  });
+
+  it('should create debug condition for single breakpoint', function () {
+    const list = new BreakpointList();
+    let hitCount = 0;
+    list.id2bp['bp1'] = { cond: () => { hitCount++; return true; } };
+
+    const cond = list.getDebugCondition();
+    assert.ok(cond !== null);
+    assert.ok(cond());
+    assert.strictEqual(hitCount, 1);
+  });
+
+  it('should evaluate multiple breakpoints with OR logic', function () {
+    const list = new BreakpointList();
+    let hits1 = 0, hits2 = 0;
+
+    list.id2bp['bp1'] = { cond: () => { hits1++; return false; } };
+    list.id2bp['bp2'] = { cond: () => { hits2++; return true; } };
+
+    const cond = list.getDebugCondition();
+    const result = cond();
+
+    assert.ok(result);
+    assert.strictEqual(hits1, 1);
+    assert.strictEqual(hits2, 1);
+  });
+
+  it('should remove breakpoint', function () {
+    const list = new BreakpointList();
+    list.id2bp['bp1'] = { cond: () => true };
+
+    delete list.id2bp['bp1'];
+    const cond = list.getDebugCondition();
+
+    assert.strictEqual(cond, null);
+  });
+});
+
+describe('Tool Filename Detection', function () {
+  describe('6502 tools', function () {
+    it('should detect C language', function () {
+      assert.strictEqual(getToolForFilename_6502('test.c'), 'cc65');
+      assert.strictEqual(getToolForFilename_6502('program.c'), 'cc65');
+    });
+
+    it('should detect assembly language', function () {
+      assert.strictEqual(getToolForFilename_6502('test.s'), 'ca65');
+      assert.strictEqual(getToolForFilename_6502('code.ca65'), 'ca65');
+      assert.strictEqual(getToolForFilename_6502('test.dasm'), 'dasm');
+    });
+
+    it('should detect various assembler formats', function () {
+      assert.strictEqual(getToolForFilename_6502('test.acme'), 'acme');
+      assert.strictEqual(getToolForFilename_6502('test.xa'), 'xa');
+      assert.strictEqual(getToolForFilename_6502('test.wiz'), 'wiz');
+    });
+
+    it('should detect special formats', function () {
+      assert.strictEqual(getToolForFilename_6502('test.ecs'), 'ecs');
+      assert.strictEqual(getToolForFilename_6502('test.cpp'), 'oscar64');
+      assert.strictEqual(getToolForFilename_6502('test.cc'), 'oscar64');
+      assert.strictEqual(getToolForFilename_6502('test.o64'), 'oscar64');
+    });
+
+    it('should default to dasm for unknown extensions', function () {
+      assert.strictEqual(getToolForFilename_6502('test.a'), 'dasm');
+      assert.strictEqual(getToolForFilename_6502('test.asm'), 'dasm');
+      assert.strictEqual(getToolForFilename_6502('unknown'), 'dasm');
+    });
+
+    it('should detect llvm-mos for special C files', function () {
+      assert.strictEqual(getToolForFilename_6502('test-llvm.c'), 'remote:llvm-mos');
+    });
+  });
+
+  describe('Z80 tools', function () {
+    it('should detect C language', function () {
+      assert.strictEqual(getToolForFilename_z80('test.c'), 'sdcc');
+      assert.strictEqual(getToolForFilename_z80('code.h'), 'sdcc');
+    });
+
+    it('should detect assembly language', function () {
+      assert.strictEqual(getToolForFilename_z80('test.s'), 'sdasz80');
+      assert.strictEqual(getToolForFilename_z80('test.sgb'), 'sdasgb');
+      assert.strictEqual(getToolForFilename_z80('test.ns'), 'naken');
+    });
+
+    it('should detect special formats', function () {
+      assert.strictEqual(getToolForFilename_z80('test.scc'), 'sccz80');
+      assert.strictEqual(getToolForFilename_z80('test.z'), 'zmac');
+      assert.strictEqual(getToolForFilename_z80('test.wiz'), 'wiz');
+    });
+
+    it('should default to zmac for unknown extensions', function () {
+      assert.strictEqual(getToolForFilename_z80('unknown'), 'zmac');
+    });
+  });
+
+  describe('6809 tools', function () {
+    it('should detect C language', function () {
+      assert.strictEqual(getToolForFilename_6809('test.c'), 'cmoc');
+      assert.strictEqual(getToolForFilename_6809('code.h'), 'cmoc');
+    });
+
+    it('should detect assembly language', function () {
+      assert.strictEqual(getToolForFilename_6809('test.xasm'), 'xasm6809');
+      assert.strictEqual(getToolForFilename_6809('test.lwasm'), 'lwasm');
+    });
+
+    it('should default to cmoc', function () {
+      assert.strictEqual(getToolForFilename_6809('unknown'), 'cmoc');
+    });
+  });
+});
+
+describe('Opcode Metadata', function () {
+  it('should return valid metadata for 6502 opcodes', function () {
+    // Test NOP (0xEA)
+    const nop = getOpcodeMetadata_6502(0xEA, 0);
+    assert.strictEqual(nop.opcode, 0xEA);
+    assert.ok(nop.minCycles > 0);
+    assert.ok(nop.maxCycles >= nop.minCycles);
+    assert.ok(nop.insnlength > 0);
+  });
+
+  it('should return consistent metadata for same opcode', function () {
+    const meta1 = getOpcodeMetadata_6502(0x69, 0x1000); // ADC immediate
+    const meta2 = getOpcodeMetadata_6502(0x69, 0x2000);
+
+    assert.strictEqual(meta1.opcode, meta2.opcode);
+    assert.strictEqual(meta1.minCycles, meta2.minCycles);
+    assert.strictEqual(meta1.maxCycles, meta2.maxCycles);
+    assert.strictEqual(meta1.insnlength, meta2.insnlength);
+  });
+
+  it('should handle all 256 6502 opcodes', function () {
+    for (let op = 0; op < 256; op++) {
+      const meta = getOpcodeMetadata_6502(op, 0);
+      assert.ok(meta.minCycles >= 0);
+      assert.ok(meta.maxCycles >= meta.minCycles);
+      assert.ok(meta.insnlength >= 0);
+    }
+  });
+});
+
+describe('CPU State Formatting', function () {
+  describe('6502 CPU state', function () {
+    it('should format basic CPU state', function () {
+      const state: any = {
+        PC: 0x1234,
+        SP: 0xFF,
+        A: 0x42,
+        X: 0x10,
+        Y: 0x20,
+        N: false, V: false, D: false, Z: false, C: false, I: false, R: true
+      };
+
+      const output = cpuStateToLongString_6502(state);
+      assert.ok(output.includes('1234')); // PC
+      assert.ok(output.includes('FF'));   // SP
+    });
+
+    it('should show flag status', function () {
+      const state1: any = {
+        PC: 0,
+        SP: 0,
+        N: true, V: false, D: false, Z: true, C: false, I: false, R: true
+      };
+
+      const output = cpuStateToLongString_6502(state1);
+      assert.ok(output.includes('N'));
+      assert.ok(output.includes('Z'));
+    });
+
+    it('should show BUSY status when R is false', function () {
+      const state: any = { PC: 0, SP: 0, R: false };
+      const output = cpuStateToLongString_6502(state);
+      assert.ok(output.includes('BUSY'));
+    });
+  });
+
+  describe('Z80 CPU state', function () {
+    it('should format Z80 state', function () {
+      const state: any = {
+        PC: 0x4000,
+        SP: 0x9000,
+        AF: 0x1234,
+        BC: 0x5678,
+        DE: 0x9ABC,
+        HL: 0xDEF0,
+        IX: 0x0001,
+        IY: 0x0002,
+        IR: 0x3344,
+        iff1: true,
+        iff2: false
+      };
+
+      const output = cpuStateToLongString_Z80(state);
+      assert.ok(output.includes('4000')); // PC
+      assert.ok(output.includes('9000')); // SP
+      assert.ok(output.includes('1234')); // AF
+    });
+  });
+
+  describe('6809 CPU state', function () {
+    it('should format 6809 state', function () {
+      const state: any = {
+        PC: 0x1000,
+        SP: 0x2000,
+        DP: 0x00,
+        A: 0x11,
+        B: 0x22,
+        X: 0x3333,
+        Y: 0x4444,
+        U: 0x5555,
+        CC: 0xF0
+      };
+
+      const output = cpuStateToLongString_6809(state);
+      assert.ok(output.includes('1000')); // PC
+      assert.ok(output.includes('2000')); // SP
+      assert.ok(output.includes('11'));   // A
+    });
+  });
+});
+
+describe('Symbol lookup', function () {
+  it('should find symbol at address', function () {
+    const platform: any = {
+      debugSymbols: new DebugSymbols({ main: 0x1000, loop: 0x1010 }, {}),
+      readAddress: (addr: number) => addr & 0xFF
+    };
+
+    const result = lookupSymbol(platform, 0x1010, false);
+    assert.ok(result.includes('loop'));
+  });
+
+  it('should find symbol before address when extra is true', function () {
+    const platform: any = {
+      debugSymbols: new DebugSymbols({ main: 0x1000 }, {}),
+      readAddress: (addr: number) => 0
+    };
+
+    const result = lookupSymbol(platform, 0x1005, true);
+    assert.ok(result.includes('main'));
+    assert.ok(result.includes('$05'));
+  });
+
+  it('should return empty string when no symbol found', function () {
+    const platform: any = {
+      debugSymbols: new DebugSymbols({}, {}),
+      readAddress: (addr: number) => 0
+    };
+
+    const result = lookupSymbol(platform, 0x5000, false);
+    assert.strictEqual(result, '');
+  });
+
+  it('should handle missing debug symbols', function () {
+    const platform: any = { debugSymbols: null };
+
+    const result = lookupSymbol(platform, 0x1000, false);
+    assert.strictEqual(result, '');
+  });
+});
+
+describe('Stack dumping', function () {
+  it('should dump stack memory', function () {
+    const mem = new Uint8Array([
+      0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+      0x20, 0x10, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D,
+    ]);
+
+    const platform: any = {
+      debugSymbols: new DebugSymbols({ func: 0x100E }, {}),
+      readAddress: (addr: number) => addr < mem.length ? mem[addr] : 0
+    };
+
+    const result = dumpStackToString(platform, mem, 0, 15, 9, 0x20);
+    assert.ok(result.includes('$'));
+    assert.ok(result.length > 0);
+  });
+
+  it('should handle big endian byte order', function () {
+    const mem = new Uint8Array([0x10, 0x20, 0x30, 0x40]);
+    const platform: any = {
+      debugSymbols: new DebugSymbols({}, {}),
+      readAddress: (addr: number) => mem[addr]
+    };
+
+    const result = dumpStackToString(platform, mem, 0, 3, 2, 0, true);
+    assert.ok(result.includes('$'));
+  });
+
+  it('should show JSR addresses', function () {
+    const mem = new Uint8Array(256);
+    // Set up JSR at 0x100 (6502 JSR is 0x20)
+    mem[0x100] = 0x20;
+    // Stack has return address pointing near 0x100
+    mem[0x50] = 0xFE;
+    mem[0x51] = 0x01;
+
+    const platform: any = {
+      debugSymbols: new DebugSymbols({ func: 0x0100 }, {}),
+      readAddress: (addr: number) => {
+        if (addr < mem.length) return mem[addr];
+        return 0;
+      }
+    };
+
+    const result = dumpStackToString(platform, mem, 0, 255, 0x50, 0x20);
+    // The function returns a string with stack content
+    assert.ok(result.includes('$'));
+  });
+});
+
+describe('BasePlatform', function () {
+  class TestPlatform extends BasePlatform {
+    loadState(state: EmuState): void { }
+    saveState(): EmuState { return {}; }
+    pause(): void { }
+    resume(): void { }
+    advance(novideo?: boolean): number { return 0; }
+  }
+
+  it('should initialize with empty internal files', function () {
+    const platform = new TestPlatform();
+    assert.deepStrictEqual(platform.internalFiles, {});
+  });
+
+  it('should set and get recorder', function () {
+    const platform = new TestPlatform();
+    const recorder: any = { frameRequested: () => false };
+    platform.setRecorder(recorder);
+    assert.strictEqual(platform.recorder, recorder);
+  });
+
+  it('should read and write files', function () {
+    const platform = new TestPlatform();
+    const data: any = { data: [1, 2, 3] };
+
+    platform.writeFile('test.txt', data);
+    const read = platform.readFile('test.txt');
+
+    assert.deepStrictEqual(read, data);
+  });
+
+  it('should return undefined for non-existent file', function () {
+    const platform = new TestPlatform();
+    const read = platform.readFile('nonexistent.txt');
+    assert.strictEqual(read, undefined);
+  });
+
+  it('should generate debug tree', function () {
+    const platform = new TestPlatform();
+    platform.debugSymbols = new DebugSymbols({ test: 0x1000 }, { info: 'test' });
+
+    const tree: any = platform.getDebugTree();
+    assert.ok(tree.state);
+    assert.deepStrictEqual(tree.debuginfo, { info: 'test' });
+  });
+});
+
+describe('BaseDebugPlatform', function () {
+  class TestDebugPlatform extends BaseDebugPlatform {
+    loadState(state: EmuState): void { }
+    saveState(): EmuState { return { c: { PC: 0 } }; }
+    pause(): void { }
+    resume(): void { }
+    advance(novideo?: boolean): number { return 0; }
+    getCPUState(): CpuState { return { PC: 0x1000, SP: 0x100 }; }
+    getSP(): number { return 0x100; }
+    getPC(): number { return 0x1000; }
+    isStable(): boolean { return true; }
+  }
+
+  it('should manage breakpoints', function () {
+    const platform = new TestDebugPlatform();
+    const cond = () => true;
+
+    platform.setBreakpoint('bp1', cond);
+    assert.ok(platform.hasBreakpoint('bp1'));
+
+    platform.clearBreakpoint('bp1');
+    assert.ok(!platform.hasBreakpoint('bp1'));
+  });
+
+  it('should clear all debug state', function () {
+    const platform = new TestDebugPlatform();
+    platform.debugSavedState = { c: { PC: 0 } };
+    platform.debugBreakState = { c: { PC: 100 } };
+    platform.onBreakpointHit = () => { };
+
+    platform.clearDebug();
+
+    assert.strictEqual(platform.debugSavedState, null);
+    assert.strictEqual(platform.debugBreakState, null);
+    assert.strictEqual(platform.onBreakpointHit, null);
+  });
+
+  it('should track frame count', function () {
+    const platform = new TestDebugPlatform();
+    assert.strictEqual(platform.frameCount, 0);
+
+    platform.postFrame();
+    assert.strictEqual(platform.frameCount, 1);
+
+    platform.postFrame();
+    assert.strictEqual(platform.frameCount, 2);
+  });
+
+  it('should detect breakpoint hits', function () {
+    const platform = new TestDebugPlatform();
+    assert.ok(!platform.wasBreakpointHit());
+
+    platform.debugBreakState = { c: { PC: 0 } };
+    assert.ok(platform.wasBreakpointHit());
+  });
+});
+
+describe('Base6502Platform', function () {
+  class TestNES6502 extends Base6502Platform {
+    loadState(state: EmuState): void { }
+    saveState(): EmuState { return { c: { PC: 0, SP: 0 } }; }
+    pause(): void { }
+    resume(): void { }
+    advance(novideo?: boolean): number { return 0; }
+    getCPUState(): CpuState { return { PC: 0x8000, SP: 0xFF }; }
+    getSP(): number { return 0xFF; }
+    getPC(): number { return 0x8000; }
+    isStable(): boolean { return true; }
+    readAddress(addr: number): number { return 0; }
+  }
+
+  it('should get default extensions', function () {
+    const platform = new TestNES6502();
+    const exts = platform.getDefaultExtensions();
+    assert.ok(exts.includes('.c'));
+    assert.ok(exts.includes('.ca65'));
+    assert.ok(exts.includes('.dasm'));
+  });
+
+  it('should get 6502 opcode metadata', function () {
+    const platform = new TestNES6502();
+    const meta = platform.getOpcodeMetadata(0x69, 0);
+    assert.ok(meta.minCycles > 0);
+  });
+
+  it('should get origin PC from reset vector', function () {
+    const platform = new TestNES6502();
+    const originPC = platform.getOriginPC();
+    assert.ok(typeof originPC === 'number');
+  });
+
+  it('should apply PC delta correction', function () {
+    const platform = new TestNES6502();
+    const state: CpuState = { PC: 0x1000 };
+
+    const fixed = platform.fixPC(state);
+    assert.strictEqual(fixed.PC, 0x0FFF); // PC - 1
+
+    const unfixed = platform.unfixPC(fixed);
+    assert.strictEqual(unfixed.PC, 0x1000);
+  });
+
+  it('should handle PC wrapping at 16-bit boundary', function () {
+    const platform = new TestNES6502();
+    const state: CpuState = { PC: 0x0000 };
+
+    const fixed = platform.fixPC(state);
+    assert.strictEqual(fixed.PC, 0xFFFF);
+  });
+
+  it('should get debug categories', function () {
+    const platform = new TestNES6502();
+    const cats = platform.getDebugCategories();
+    assert.ok(cats.includes('CPU'));
+    assert.ok(cats.includes('Stack'));
+  });
+});
+
+describe('inspectSymbol', function () {
+  it('should inspect symbol value at address', function () {
+    const platform: any = {
+      debugSymbols: new DebugSymbols({ myvar: 0x100 }, {}),
+      readAddress: (addr: number) => addr === 0x100 ? 0x42 : 0x00
+    };
+
+    const result = inspectSymbol(platform, 'myvar');
+    assert.ok(result.includes('100'));
+    assert.ok(result.includes('42'));
+  });
+
+  it('should handle two-byte values', function () {
+    const platform: any = {
+      debugSymbols: new DebugSymbols({ word: 0x200 }, {}),
+      readAddress: (addr: number) => {
+        if (addr === 0x200) return 0x34;
+        if (addr === 0x201) return 0x12;
+        return 0;
+      }
+    };
+
+    const result = inspectSymbol(platform, 'word');
+    assert.ok(result.includes('200'));
+  });
+
+  it('should look for C and asm symbol variants', function () {
+    const platform: any = {
+      debugSymbols: new DebugSymbols({ _myvar: 0x300 }, {}),
+      readAddress: (addr: number) => addr === 0x300 ? 0x99 : 0
+    };
+
+    const result = inspectSymbol(platform, 'myvar');
+    assert.ok(result.includes('99'));
+  });
+
+  it('should return undefined for missing symbol', function () {
+    const platform: any = {
+      debugSymbols: new DebugSymbols({}, {}),
+      readAddress: (addr: number) => 0
+    };
+
+    const result = inspectSymbol(platform, 'nonexistent');
+    assert.ok(result === undefined || result === null);
+  });
+
+  it('should handle missing debug symbols', function () {
+    const platform: any = { debugSymbols: null };
+    const result = inspectSymbol(platform, 'symbol');
+    assert.strictEqual(result, undefined);
+  });
+
+  it('should handle missing readAddress method', function () {
+    const platform: any = {
+      debugSymbols: new DebugSymbols({ test: 0x100 }, {}),
+      readAddress: undefined
+    };
+
+    const result = inspectSymbol(platform, 'test');
+    assert.ok(result === null);
+  });
+});
+
diff --git a/test/unit/testcommon.ts b/test/unit/testcommon.ts
new file mode 100644
index 00000000..b6287458
--- /dev/null
+++ b/test/unit/testcommon.ts
@@ -0,0 +1,256 @@
+
+import assert from "assert";
+import { describe, it } from "mocha";
+import {
+  lpad, rpad, byte2signed, getFilenameForPath, getFolderForPath,
+  getFilenamePrefix, hex, tobin, toradix, arrayCompare, invertMap,
+  stringToByteArray, byteArrayToString, byteArrayToUTF8, removeBOM,
+  isProbablyBinary, clamp, safeident, rgb2bgr, RGBA, findIntegerFactors,
+  replaceAll, highlightDifferences, decodeQueryString, parseBool,
+  safe_extend, printFlags, byteToASCII, coerceToArray
+} from "../../src/common/util";
+
+describe('String Padding Functions', function () {
+  it('lpad should pad strings on the left', function () {
+    assert.strictEqual(lpad('5', 3), '  5');
+    assert.strictEqual(lpad('hello', 8), '   hello');
+    assert.strictEqual(lpad('x', 1), 'x');
+    assert.strictEqual(lpad('123', 5), '  123');
+  });
+
+  it('rpad should pad strings on the right', function () {
+    assert.strictEqual(rpad('5', 3), '5  ');
+    assert.strictEqual(rpad('hello', 8), 'hello   ');
+    assert.strictEqual(rpad('x', 1), 'x');
+    assert.strictEqual(rpad('123', 5), '123  ');
+  });
+});
+
+describe('Number Conversion Functions', function () {
+  it('hex should format numbers in hexadecimal', function () {
+    assert.strictEqual(hex(255), 'FF');
+    assert.strictEqual(hex(0), '00');
+    assert.strictEqual(hex(255, 4), '00FF');
+    assert.strictEqual(hex(65535, 4), 'FFFF');
+    assert.strictEqual(hex(0x12345678, 8), '12345678');
+    assert.strictEqual(hex(15, 2), '0F');
+  });
+
+  it('tobin should format numbers in binary', function () {
+    assert.strictEqual(tobin(0), '00000000');
+    assert.strictEqual(tobin(255), '11111111');
+    assert.strictEqual(tobin(5), '00000101');
+    assert.strictEqual(tobin(15, 4), '1111');
+    assert.strictEqual(tobin(128), '10000000');
+  });
+
+  it('toradix should convert to various bases', function () {
+    assert.strictEqual(toradix(10, 4, 16), '000A');
+    assert.strictEqual(toradix(255, 8, 16), '000000FF');
+    assert.strictEqual(toradix(7, 3, 2), '111');
+    assert.strictEqual(toradix(100, 4, 10), '0100');
+  });
+
+  it('byte2signed should convert unsigned to signed bytes', function () {
+    assert.strictEqual(byte2signed(0), 0);
+    assert.strictEqual(byte2signed(127), 127);
+    assert.strictEqual(byte2signed(128), -128);
+    assert.strictEqual(byte2signed(255), -1);
+    assert.strictEqual(byte2signed(200), -56);
+    assert.strictEqual(byte2signed(0x80), -128);
+  });
+});
+
+describe('File Path Functions', function () {
+  it('getFilenameForPath should extract filename from path', function () {
+    assert.strictEqual(getFilenameForPath('path/to/file.txt'), 'file.txt');
+    assert.strictEqual(getFilenameForPath('file.txt'), 'file.txt');
+    assert.strictEqual(getFilenameForPath('/a/b/c/d.js'), 'd.js');
+    assert.strictEqual(getFilenameForPath('a/b'), 'b');
+  });
+
+  it('getFolderForPath should extract folder from path', function () {
+    assert.strictEqual(getFolderForPath('path/to/file.txt'), 'path/to');
+    assert.strictEqual(getFolderForPath('file.txt'), '');
+    assert.strictEqual(getFolderForPath('/a/b/c/d.js'), '/a/b/c');
+    assert.strictEqual(getFolderForPath('a/b/c'), 'a/b');
+  });
+
+  it('getFilenamePrefix should extract name without extension', function () {
+    assert.strictEqual(getFilenamePrefix('file.txt'), 'file');
+    assert.strictEqual(getFilenamePrefix('archive.tar.gz'), 'archive.tar');
+    assert.strictEqual(getFilenamePrefix('noext'), 'noext');
+    assert.strictEqual(getFilenamePrefix('.hidden'), '.hidden');
+  });
+});
+
+describe('Array/Collection Functions', function () {
+  it('arrayCompare should compare arrays', function () {
+    assert.ok(arrayCompare([1, 2, 3], [1, 2, 3]));
+    assert.ok(!arrayCompare([1, 2, 3], [1, 2, 4]));
+    assert.ok(!arrayCompare([1, 2], [1, 2, 3]));
+    assert.ok(arrayCompare([], []));
+    assert.ok(!arrayCompare([1], []));
+    assert.ok(arrayCompare(null, null));
+    assert.ok(!arrayCompare(null, [1]));
+    assert.ok(!arrayCompare([1], null));
+    const arr1 = new Uint8Array([1, 2, 3]);
+    const arr2 = new Uint8Array([1, 2, 3]);
+    assert.ok(arrayCompare(arr1, arr2));
+  });
+
+  it('invertMap should invert key-value pairs', function () {
+    const map = { a: '1', b: '2', c: '3' };
+    const inv = invertMap(map);
+    assert.strictEqual(inv['1'], 'a');
+    assert.strictEqual(inv['2'], 'b');
+    assert.strictEqual(inv['3'], 'c');
+  });
+
+  it('coerceToArray should convert various types to arrays', function () {
+    assert.deepStrictEqual(coerceToArray([1, 2, 3]), [1, 2, 3]);
+    assert.deepStrictEqual(coerceToArray({ a: 1, b: 2 }), [1, 2]);
+  });
+});
+
+describe('Byte Array Conversion Functions', function () {
+  it('stringToByteArray should convert string to bytes', function () {
+    const bytes = stringToByteArray('hello');
+    assert.strictEqual(bytes.length, 5);
+    assert.strictEqual(bytes[0], 104); // 'h'
+    assert.strictEqual(bytes[4], 111); // 'o'
+  });
+
+  it('byteArrayToString should convert bytes to string', function () {
+    const bytes = [72, 101, 108, 108, 111]; // "Hello"
+    assert.strictEqual(byteArrayToString(bytes), 'Hello');
+    assert.strictEqual(byteArrayToString(new Uint8Array([65, 66, 67])), 'ABC');
+  });
+
+  it('byteArrayToUTF8 should decode UTF-8', function () {
+    const ascii = byteArrayToUTF8([72, 101, 108, 108, 111]);
+    assert.strictEqual(ascii, 'Hello');
+  });
+
+  it('removeBOM should strip BOM if present', function () {
+    assert.strictEqual(removeBOM('hello'), 'hello');
+    assert.strictEqual(removeBOM('hello'), 'hello');
+  });
+});
+
+describe('Binary Detection', function () {
+  it('isProbablyBinary should detect binary data', function () {
+    assert.ok(!isProbablyBinary('test.txt', [104, 101, 108, 108, 111])); // "hello"
+    assert.ok(isProbablyBinary('test.bin', [1, 2, 3]));
+    assert.ok(isProbablyBinary('test.chr', [255, 255]));
+    assert.ok(isProbablyBinary('test.dat', [0]));
+    assert.ok(!isProbablyBinary('test.c', [47, 47, 105, 102])); // "//if"
+    assert.ok(isProbablyBinary(null, [0, 0, 0, 0])); // null bytes
+  });
+});
+
+describe('Color Functions', function () {
+  it('rgb2bgr should swap red and blue channels', function () {
+    assert.strictEqual(rgb2bgr(0xFF0000), 0x0000FF);
+    assert.strictEqual(rgb2bgr(0x00FF00), 0x00FF00);
+    assert.strictEqual(rgb2bgr(0x0000FF), 0xFF0000);
+    assert.strictEqual(rgb2bgr(0xFFFFFF), 0xFFFFFF);
+  });
+
+  it('RGBA should create color value', function () {
+    const white = RGBA(255, 255, 255);
+    assert.strictEqual(white & 0xFFFFFF, 0xFFFFFF);
+    const black = RGBA(0, 0, 0);
+    assert.strictEqual(black & 0xFFFFFF, 0x000000);
+  });
+
+  it('clamp should constrain values', function () {
+    assert.strictEqual(clamp(0, 10, 5), 5);
+    assert.strictEqual(clamp(0, 10, -5), 0);
+    assert.strictEqual(clamp(0, 10, 15), 10);
+    assert.strictEqual(clamp(1, 1, 5), 1);
+  });
+});
+
+describe('String Manipulation', function () {
+  it('safeident should create valid identifiers', function () {
+    assert.strictEqual(safeident('valid_name'), 'valid_name');
+    assert.strictEqual(safeident('123abc'), '_123abc');
+    assert.strictEqual(safeident('-name'), '__name');
+    assert.strictEqual(safeident('name-with-dashes'), 'name_with_dashes');
+    assert.strictEqual(safeident('name@#$%'), 'name_');
+  });
+
+  it('replaceAll should replace all occurrences', function () {
+    assert.strictEqual(replaceAll('aaa', 'a', 'b'), 'bbb');
+    assert.strictEqual(replaceAll('hello world', ' ', '-'), 'hello-world');
+    assert.strictEqual(replaceAll('test', 'x', 'y'), 'test');
+    assert.strictEqual(replaceAll('', 'a', 'b'), '');
+  });
+
+  it('byteToASCII should convert bytes to readable chars', function () {
+    assert.strictEqual(byteToASCII(65), 'A');
+    assert.strictEqual(byteToASCII(32), ' ');
+    assert.strictEqual(byteToASCII(0), '␀'); // NULL control char
+  });
+});
+
+describe('Query String Functions', function () {
+  it('decodeQueryString should parse query parameters', function () {
+    const qs1 = decodeQueryString('?key=value&foo=bar');
+    assert.strictEqual(qs1['key'], 'value');
+    assert.strictEqual(qs1['foo'], 'bar');
+
+    const qs2 = decodeQueryString('a=1&b=2');
+    assert.strictEqual(qs2['a'], '1');
+    assert.strictEqual(qs2['b'], '2');
+
+    const qs3 = decodeQueryString('key=value+with+spaces');
+    assert.ok(qs3['key'].includes(' '));
+  });
+
+  it('parseBool should parse boolean strings', function () {
+    assert.ok(parseBool('true'));
+    assert.ok(parseBool('1'));
+    assert.ok(parseBool('yes'));
+    assert.ok(!parseBool('false'));
+    assert.ok(!parseBool('0'));
+    assert.ok(!parseBool(''));
+  });
+});
+
+describe('Complex Utility Functions', function () {
+  it('findIntegerFactors should find factor pairs', function () {
+    const f1 = findIntegerFactors(64, 1, 1, 1);
+    assert.ok(f1.a >= f1.b);
+    assert.strictEqual(f1.a * f1.b >= 64, true);
+
+    const f2 = findIntegerFactors(100, 5, 5, 1);
+    assert.ok(f2.a >= 5);
+    assert.ok(f2.b >= 5);
+  });
+
+  it('safe_extend should copy primitive values and arrays', function () {
+    const dest = { x: 1 };
+    const src = { y: 2, arr: [1, 2, 3] };
+    safe_extend(false, dest, src);
+    assert.strictEqual(dest['x'], 1);
+    assert.strictEqual(dest['y'], 2);
+    assert.deepStrictEqual(dest['arr'], [1, 2, 3]);
+    assert.ok(dest['arr'] !== src['arr']); // should be copy
+  });
+
+  it('printFlags should format flag values', function () {
+    const names = ['CARRY', 'ZERO', 'IRQ_DISABLE', 'DECIMAL'];
+    const result = printFlags(0x01, names, false);
+    assert.ok(result.includes('CARRY'));
+    const result2 = printFlags(0x00, names, false);
+    assert.ok(result2.includes('-'));
+  });
+
+  it('highlightDifferences should mark changes in text', function () {
+    const diff = highlightDifferences('hello world', 'hello there');
+    assert.ok(diff.includes('hilite'));
+  });
+});
+
diff --git a/test/unit/testcommon_ext.ts b/test/unit/testcommon_ext.ts
new file mode 100644
index 00000000..ec3186e8
--- /dev/null
+++ b/test/unit/testcommon_ext.ts
@@ -0,0 +1,361 @@
+
+import assert from "assert";
+import { describe, it } from "mocha";
+import {
+  rgbToPixel, DMG_PALETTE, DMG_PALETTE_RGB, DMG_PALETTE_RGB24, dmgShadeFromRgb
+} from "../../src/common/gbpalette";
+import { SourceFile } from "../../src/common/workertypes";
+import { ProbeRecorder, ProbeFlags } from "../../src/common/probe";
+
+describe('Game Boy Palette Functions', function () {
+  it('rgbToPixel should convert RGB to packed pixel format', function () {
+    const white = rgbToPixel(255, 255, 255);
+    assert.strictEqual(white & 0xFFFFFF, 0xFFFFFF);
+    assert.strictEqual((white >> 24) & 0xFF, 0xFF); // alpha
+
+    const black = rgbToPixel(0, 0, 0);
+    assert.strictEqual(black & 0xFFFFFF, 0x000000);
+
+    const red = rgbToPixel(255, 0, 0);
+    assert.strictEqual(red & 0xFF, 255); // red channel
+    assert.strictEqual((red >> 8) & 0xFF, 0); // green channel
+    assert.strictEqual((red >> 16) & 0xFF, 0); // blue channel
+  });
+
+  it('DMG_PALETTE should contain 4 shades', function () {
+    assert.strictEqual(DMG_PALETTE.length, 4);
+    // Should be in light to dark order
+    assert.ok(DMG_PALETTE[0] > DMG_PALETTE[3]); // lightest > darkest numerically
+  });
+
+  it('DMG_PALETTE_RGB should match DMG_PALETTE', function () {
+    assert.strictEqual(DMG_PALETTE_RGB.length, 4);
+    for (let i = 0; i < 4; i++) {
+      const [r, g, b] = DMG_PALETTE_RGB[i];
+      const expected = rgbToPixel(r, g, b);
+      assert.strictEqual(DMG_PALETTE[i], expected);
+    }
+  });
+
+  it('DMG_PALETTE_RGB24 should be RGB values without alpha', function () {
+    assert.strictEqual(DMG_PALETTE_RGB24.length, 4);
+    assert.strictEqual(DMG_PALETTE_RGB24[0], 0xd0d884); // lightest
+    assert.strictEqual(DMG_PALETTE_RGB24[3], 0x2d3122); // darkest
+  });
+
+  it('dmgShadeFromRgb should map greyscale to shade index', function () {
+    // Very light colors should map to shade 0
+    assert.strictEqual(dmgShadeFromRgb(255, 255, 255), 0);
+    assert.strictEqual(dmgShadeFromRgb(200, 200, 200), 0);
+
+    // Medium-light should be shade 1
+    assert.strictEqual(dmgShadeFromRgb(128, 128, 128), 1);
+
+    // Medium-dark should be shade 2
+    assert.strictEqual(dmgShadeFromRgb(80, 80, 80), 2);
+
+    // Very dark should be shade 3
+    assert.strictEqual(dmgShadeFromRgb(0, 0, 0), 3);
+    assert.strictEqual(dmgShadeFromRgb(30, 30, 30), 3);
+  });
+
+  it('dmgShadeFromRgb should work with non-greyscale colors', function () {
+    // Red (255,0,0) avg=85 → 2
+    assert.strictEqual(dmgShadeFromRgb(255, 0, 0), 2);
+    // Red (128,0,0) avg≈43 → 3
+    assert.strictEqual(dmgShadeFromRgb(128, 0, 0), 3);
+
+    // Green (0,255,0) avg=85 → 2
+    assert.strictEqual(dmgShadeFromRgb(0, 255, 0), 2);
+    // Green (0,128,0) avg≈43 → 3
+    assert.strictEqual(dmgShadeFromRgb(0, 128, 0), 3);
+
+    // Blue (0,0,255) avg=85 → 2
+    assert.strictEqual(dmgShadeFromRgb(0, 0, 255), 2);
+    // Blue (0,0,128) avg≈43 → 3
+    assert.strictEqual(dmgShadeFromRgb(0, 0, 128), 3);
+  });
+
+  it('dmgShadeFromRgb thresholds should be accurate', function () {
+    // Test boundary at 192
+    assert.strictEqual(dmgShadeFromRgb(192, 192, 192), 0);
+    assert.strictEqual(dmgShadeFromRgb(191, 191, 191), 1);
+
+    // Test boundary at 128
+    assert.strictEqual(dmgShadeFromRgb(128, 128, 128), 1);
+    assert.strictEqual(dmgShadeFromRgb(127, 127, 127), 2);
+
+    // Test boundary at 64
+    assert.strictEqual(dmgShadeFromRgb(64, 64, 64), 2);
+    assert.strictEqual(dmgShadeFromRgb(63, 63, 63), 3);
+  });
+});
+
+describe('SourceFile Class', function () {
+  it('should create SourceFile with lines and text', function () {
+    const lines = [
+      { line: 1, offset: 0, insns: 'LDA #$00' },
+      { line: 2, offset: 2, insns: 'STA $80' },
+      { line: 3, offset: 4, insns: 'RTS' },
+    ];
+    const text = 'LDA #$00\nSTA $80\nRTS\n';
+    const sf = new SourceFile(lines, text);
+
+    assert.strictEqual(sf.lines.length, 3);
+    assert.strictEqual(sf.text, text);
+  });
+
+  it('should build offset to line mapping', function () {
+    const lines = [
+      { line: 1, offset: 0, insns: 'LDA #$00' },
+      { line: 2, offset: 2, insns: 'STA $80' },
+      { line: 3, offset: 4, insns: 'RTS' },
+    ];
+    const sf = new SourceFile(lines, '');
+
+    assert.ok(sf.offset2loc[0]);
+    assert.ok(sf.offset2loc[2]);
+    assert.ok(sf.offset2loc[4]);
+  });
+
+  it('should build line to offset mapping', function () {
+    const lines = [
+      { line: 1, offset: 0 },
+      { line: 2, offset: 2 },
+      { line: 3, offset: 4 },
+    ];
+    const sf = new SourceFile(lines, '');
+
+    assert.strictEqual(sf.line2offset[1], 0);
+    assert.strictEqual(sf.line2offset[2], 2);
+    assert.strictEqual(sf.line2offset[3], 4);
+  });
+
+  it('should handle negative offsets gracefully', function () {
+    const lines = [
+      { line: 1, offset: -1 },
+      { line: 2, offset: 0 },
+      { line: 3, offset: 2 },
+    ];
+    const sf = new SourceFile(lines, '');
+
+    // Negative offsets should not be added to mapping
+    assert.ok(!sf.offset2loc[-1]);
+    assert.ok(sf.offset2loc[0]);
+  });
+
+  it('findLineForOffset should locate source line by address', function () {
+    const lines = [
+      { line: 1, offset: 0, insns: 'LDA #$00' },
+      { line: 2, offset: 2, insns: 'STA $80' },
+      { line: 3, offset: 4, insns: 'RTS' },
+    ];
+    const sf = new SourceFile(lines, '');
+
+    const line0 = sf.findLineForOffset(0, 0);
+    assert.strictEqual(line0.line, 1);
+    assert.strictEqual(line0.offset, 0);
+
+    const line2 = sf.findLineForOffset(2, 0);
+    assert.strictEqual(line2.line, 2);
+    assert.strictEqual(line2.offset, 2);
+  });
+
+  it('findLineForOffset should look behind for nearest line', function () {
+    const lines = [
+      { line: 1, offset: 0, insns: 'LDA #$00' },
+      { line: 2, offset: 2, insns: 'STA $80' },
+      { line: 3, offset: 4, insns: 'RTS' },
+    ];
+    const sf = new SourceFile(lines, '');
+
+    // Looking for offset 3 with lookbehind=1 should find offset 2
+    const line = sf.findLineForOffset(3, 1);
+    assert.strictEqual(line.line, 2);
+    assert.strictEqual(line.offset, 2);
+  });
+
+  it('findLineForOffset should return null if not found', function () {
+    const lines = [
+      { line: 1, offset: 0 },
+      { line: 2, offset: 2 },
+    ];
+    const sf = new SourceFile(lines, '');
+
+    // Looking for offset 10 should not find anything
+    const line = sf.findLineForOffset(10, 0);
+    assert.strictEqual(line, null);
+  });
+
+  it('lineCount should return number of lines', function () {
+    const lines = [
+      { line: 1, offset: 0 },
+      { line: 2, offset: 2 },
+      { line: 3, offset: 4 },
+    ];
+    const sf = new SourceFile(lines, '');
+
+    assert.strictEqual(sf.lineCount(), 3);
+  });
+
+  it('should handle duplicate offsets (first wins)', function () {
+    const lines = [
+      { line: 1, offset: 0, insns: 'LDA #$00' },
+      { line: 2, offset: 0, insns: 'STA $80' }, // Same offset
+      { line: 3, offset: 2, insns: 'RTS' },
+    ];
+    const sf = new SourceFile(lines, '');
+
+    // First line at offset 0 should be returned
+    const line = sf.findLineForOffset(0, 0);
+    assert.strictEqual(line.line, 1);
+  });
+});
+
+describe('ProbeRecorder Class', function () {
+  class MockMachine {
+    probe: any;
+    connectProbe(probe) {
+      this.probe = probe;
+    }
+  }
+
+  it('should create ProbeRecorder with buffer', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 1024);
+
+    assert.ok(pr.buf);
+    assert.strictEqual(pr.buf.length, 1024);
+    assert.strictEqual(pr.idx, 0);
+  });
+
+  it('should log data to buffer', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 100);
+
+    pr.log(0x12000080); // MEM_READ at address 0x80
+    assert.strictEqual(pr.idx, 1);
+    assert.strictEqual(pr.buf[0], 0x12000080);
+
+    pr.log(0x13000081); // MEM_WRITE at address 0x81
+    assert.strictEqual(pr.idx, 2);
+    assert.strictEqual(pr.buf[1], 0x13000081);
+  });
+
+  it('should not exceed buffer length', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 2);
+
+    pr.log(0x12000080);
+    pr.log(0x13000081);
+    pr.log(0x14000082); // Should not write (buffer full)
+
+    assert.strictEqual(pr.idx, 2);
+    assert.strictEqual(pr.buf[0], 0x12000080);
+    assert.strictEqual(pr.buf[1], 0x13000081);
+  });
+
+  it('should retrieve last operation', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 100);
+
+    pr.log(0x12000080);
+    pr.log(0x13000081);
+
+    const lastOp = pr.lastOp();
+    assert.strictEqual(lastOp, 0x13000000); // MEM_WRITE flag
+  });
+
+  it('should retrieve last address', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 100);
+
+    pr.log(0x12000080);
+    pr.log(0x13AABBCC);
+
+    const lastAddr = pr.lastAddr();
+    assert.strictEqual(lastAddr, 0xAABBCC);
+  });
+
+  it('should return -1 for lastOp on empty buffer', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 100);
+
+    const lastOp = pr.lastOp();
+    assert.strictEqual(lastOp, -1);
+  });
+
+  it('should clear buffer', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 100);
+
+    pr.log(0x12000080);
+    pr.log(0x13000081);
+    assert.strictEqual(pr.idx, 2);
+
+    pr.clear();
+    assert.strictEqual(pr.idx, 0);
+  });
+
+  it('should reset buffer', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 100);
+
+    pr.log(0x12000080);
+    assert.strictEqual(pr.buf.length, 100);
+
+    pr.reset(200);
+    assert.strictEqual(pr.buf.length, 200);
+    assert.strictEqual(pr.idx, 0);
+  });
+
+  it('should relog last entry', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 100);
+
+    pr.log(0x12000080);
+    pr.relog(0x13000080);
+
+    assert.strictEqual(pr.idx, 1);
+    assert.strictEqual(pr.buf[0], 0x13000080);
+  });
+
+  it('should track scanline', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 100);
+
+    assert.strictEqual(pr.sl, 0);
+    pr.sl = 100;
+    assert.strictEqual(pr.sl, 100);
+  });
+
+  it('should track stack pointer', function () {
+    const machine = new MockMachine();
+    const pr = new ProbeRecorder(machine, 100);
+
+    assert.strictEqual(pr.cur_sp, -1);
+    pr.cur_sp = 0xFF;
+    assert.strictEqual(pr.cur_sp, 0xFF);
+  });
+});
+
+describe('ProbeFlags Enumeration', function () {
+  it('should have correct flag values', function () {
+    assert.strictEqual(ProbeFlags.CLOCKS, 0x00000000);
+    assert.strictEqual(ProbeFlags.EXECUTE, 0x01000000);
+    assert.strictEqual(ProbeFlags.INTERRUPT, 0x08000000);
+    assert.strictEqual(ProbeFlags.MEM_READ, 0x12000000);
+    assert.strictEqual(ProbeFlags.MEM_WRITE, 0x13000000);
+    assert.strictEqual(ProbeFlags.FRAME, 0x7f000000);
+  });
+
+  it('should extract operation from probe value', function () {
+    const probeValue = 0x12000080;
+    const opcode = probeValue & 0xFF000000;
+    assert.strictEqual(opcode, ProbeFlags.MEM_READ);
+
+    const address = probeValue & 0xFFFFFF;
+    assert.strictEqual(address, 0x80);
+  });
+});
+
diff --git a/test/unit/testemu.ts b/test/unit/testemu.ts
new file mode 100644
index 00000000..5bc32daa
--- /dev/null
+++ b/test/unit/testemu.ts
@@ -0,0 +1,522 @@
+import assert from "assert";
+import { describe, it } from "mocha";
+import {
+  noise, getNoiseSeed, setNoiseSeed, KeyFlags, RAM, EmuHalt,
+  AnimationTimer, dumpRAM, Keys, makeKeycodeMap, newKeyboardHandler,
+  _setKeyboardEvents, padBytes, AddressDecoder, newAddressDecoder,
+  getMousePos, drawCrosshair, gtia_ntsc_to_rgb,
+} from "../../src/common/emu";
+
+describe('Noise PRNG', function () {
+  it('should produce a deterministic sequence from seed 1', function () {
+    setNoiseSeed(1);
+    const seq = [];
+    for (let i = 0; i < 8; i++) seq.push(noise());
+    assert.deepStrictEqual(seq, [33, 1, 34, 25, 250, 201, 8, 180]);
+  });
+
+  it('should track and restore the seed', function () {
+    setNoiseSeed(0x1234);
+    assert.strictEqual(getNoiseSeed(), 0x1234);
+    noise();
+    assert.notStrictEqual(getNoiseSeed(), 0x1234);
+  });
+
+  it('should return 0 forever for seed 0', function () {
+    setNoiseSeed(0);
+    assert.strictEqual(noise(), 0);
+    assert.strictEqual(noise(), 0);
+    assert.strictEqual(noise(), 0);
+    assert.strictEqual(getNoiseSeed(), 0);
+  });
+
+  it('should always return a byte', function () {
+    setNoiseSeed(1);
+    for (let i = 0; i < 100; i++) {
+      const n = noise();
+      assert.ok(n >= 0 && n <= 255);
+    }
+  });
+});
+
+describe('KeyFlags Enumeration', function () {
+  it('should have correct flag values', function () {
+    assert.strictEqual(KeyFlags.KeyDown, 1);
+    assert.strictEqual(KeyFlags.Shift, 2);
+    assert.strictEqual(KeyFlags.Ctrl, 4);
+    assert.strictEqual(KeyFlags.Alt, 8);
+    assert.strictEqual(KeyFlags.Meta, 16);
+    assert.strictEqual(KeyFlags.KeyUp, 64);
+    assert.strictEqual(KeyFlags.KeyPress, 128);
+  });
+});
+
+describe('RAM Class', function () {
+  it('should allocate zero-initialized memory', function () {
+    const ram = new RAM(16);
+    assert.ok(ram.mem instanceof Uint8Array);
+    assert.strictEqual(ram.mem.length, 16);
+    assert.strictEqual(ram.mem[0], 0);
+    assert.strictEqual(ram.mem[15], 0);
+  });
+
+  it('should allow reading and writing', function () {
+    const ram = new RAM(4);
+    ram.mem[2] = 0xAA;
+    assert.strictEqual(ram.mem[2], 0xAA);
+  });
+});
+
+describe('EmuHalt', function () {
+  it('should be an Error subclass with default properties', function () {
+    const e = new EmuHalt("Halt!");
+    assert.ok(e instanceof Error);
+    assert.ok(e instanceof EmuHalt);
+    assert.strictEqual(e.message, "Halt!");
+    assert.ok(e.squelchError);
+    assert.strictEqual(e.$loc, undefined);
+  });
+
+  it('should carry a source location', function () {
+    const e = new EmuHalt("bad opcode", { line: 42 } as any);
+    assert.deepStrictEqual(e.$loc, { line: 42 });
+  });
+
+  it('should be catchable via instanceof', function () {
+    let caught = null;
+    try {
+      throw new EmuHalt("boom");
+    } catch (err) {
+      caught = err;
+    }
+    assert.ok(caught instanceof EmuHalt);
+    assert.ok(caught instanceof Error);
+    assert.strictEqual(caught.message, "boom");
+  });
+});
+
+describe('dumpRAM', function () {
+  it('should format a Uint8Array dump', function () {
+    const ram = new Uint8Array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]);
+    assert.strictEqual(dumpRAM(ram, 0, 16),
+      "$00: 00 01 02 03 04 05 06 07  08 09 0A 0B 0C 0D 0E 0F\n");
+  });
+
+  it('should show the base offset in addresses', function () {
+    const ram = new Uint8Array([1, 2, 3]);
+    assert.strictEqual(dumpRAM(ram, 0x8000, 8),
+      "$8000: 01 02 03\n");
+  });
+
+  it('should format a Uint16Array dump', function () {
+    const ram = new Uint16Array([0x1234, 0x5678, 0x9ABC, 0xDEF0, 0x1111, 0x2222, 0x3333, 0x4444]);
+    assert.strictEqual(dumpRAM(ram, 0, 16),
+      "$00: 1234 5678 9ABC DEF0  1111 2222 3333 4444\n$08:\n");
+  });
+
+  it('should format a Float32Array dump with precision', function () {
+    const ram = new Float32Array([1.5, 2.25, 3.125, 0.5]);
+    assert.strictEqual(dumpRAM(ram, 0, 8),
+      "$00: 1.5000000 2.2500000  3.1250000 0.50000000\n$04:\n");
+  });
+
+  it('should handle plain arrays (BYTES_PER_ELEMENT fallback)', function () {
+    assert.strictEqual(dumpRAM([0x0A, 0x0B], 0, 2), "$00: 0A 0B\n");
+  });
+});
+
+describe('Keys Table', function () {
+  it('should define directional and action keys', function () {
+    assert.strictEqual(Keys.UP.c, 38);
+    assert.strictEqual(Keys.DOWN.c, 40);
+    assert.strictEqual(Keys.LEFT.c, 37);
+    assert.strictEqual(Keys.RIGHT.c, 39);
+    assert.strictEqual(Keys.A.c, 32); // Space
+    assert.strictEqual(Keys.B.c, 16); // Shift
+    assert.strictEqual(Keys.SELECT.c, 220);
+    assert.strictEqual(Keys.START.c, 13);
+    assert.strictEqual(Keys.ANYKEY.c, 0);
+  });
+
+  it('should annotate gamepad mapping metadata', function () {
+    assert.strictEqual(Keys.UP.plyr, 0);
+    assert.strictEqual(Keys.UP.button, 12);
+    assert.strictEqual(Keys.UP.yaxis, -1);
+    assert.strictEqual(Keys.RIGHT.xaxis, 1);
+    assert.strictEqual(Keys.A.button, 0);
+    assert.strictEqual(Keys.P2_UP.plyr, 1);
+    assert.strictEqual(Keys.P2_UP.c, 87); // W
+  });
+
+  it('should define function keys and misc keys', function () {
+    assert.strictEqual(Keys.VK_ESCAPE.c, 27);
+    assert.strictEqual(Keys.VK_F1.c, 112);
+    assert.strictEqual(Keys.VK_F12.c, 123);
+    assert.strictEqual(Keys.VK_ENTER.c, 13);
+    assert.strictEqual(Keys.VK_SPACE.c, 32);
+  });
+
+  it('should give every key a name and numeric code', function () {
+    const entries = Object.keys(Keys);
+    assert.ok(entries.length >= 100);
+    for (const name of entries) {
+      assert.ok(name.length > 0);
+      const def = Keys[name];
+      assert.strictEqual(typeof def.c, 'number');
+      assert.ok(def.n.length > 0, `key ${name} should have a name`);
+    }
+  });
+});
+
+describe('makeKeycodeMap', function () {
+  it('should build a map keyed by keycode', function () {
+    const map = makeKeycodeMap([[Keys.A, 0, 0x01], [Keys.B, 0, 0x02]]);
+    assert.ok(map instanceof Map);
+    assert.strictEqual(map[32].index, 0);
+    assert.strictEqual(map[32].mask, 0x01);
+    assert.strictEqual(map[32].def, Keys.A);
+    assert.strictEqual(map[16].index, 0);
+    assert.strictEqual(map[16].mask, 0x02);
+    assert.strictEqual(map[9999], undefined);
+  });
+});
+
+describe('newKeyboardHandler', function () {
+  it('should set switches on keydown and clear on keyup', function () {
+    const map = makeKeycodeMap([[Keys.A, 0, 0x01]]);
+    const switches = new Uint8Array(2);
+    const handler = newKeyboardHandler(switches, map);
+    handler(32, 0, KeyFlags.KeyDown); // A (Space)
+    assert.strictEqual(switches[0], 0x01);
+    handler(32, 0, KeyFlags.KeyDown); // idempotent
+    assert.strictEqual(switches[0], 0x01);
+    handler(32, 0, KeyFlags.KeyUp);
+    assert.strictEqual(switches[0], 0x00);
+  });
+
+  it('should support multiple keys and switch indices', function () {
+    const map = makeKeycodeMap([
+      [Keys.A, 0, 0x01],
+      [Keys.B, 0, 0x02],
+      [Keys.UP, 1, 0x80],
+    ]);
+    const switches = new Uint8Array(2);
+    const handler = newKeyboardHandler(switches, map);
+    handler(32, 0, KeyFlags.KeyDown);
+    handler(16, 0, KeyFlags.KeyDown);
+    handler(38, 0, KeyFlags.KeyDown);
+    assert.strictEqual(switches[0], 0x03);
+    assert.strictEqual(switches[1], 0x80);
+    handler(32, 0, KeyFlags.KeyUp);
+    assert.strictEqual(switches[0], 0x02);
+  });
+
+  it('should support active-low (negative mask) switches', function () {
+    const map = makeKeycodeMap([[Keys.START, 0, -0x01]]);
+    const switches = new Uint8Array(1);
+    const handler = newKeyboardHandler(switches, map);
+    switches[0] = 0x01;
+    handler(13, 0, KeyFlags.KeyDown); // active-low press clears the bit
+    assert.strictEqual(switches[0], 0x00);
+    handler(13, 0, KeyFlags.KeyUp); // release sets the bit
+    assert.strictEqual(switches[0], 0x01);
+  });
+
+  it('should fall back to ANYKEY entry for unknown keys', function () {
+    const map = makeKeycodeMap([[Keys.ANYKEY, 0, 0x40]]);
+    const switches = new Uint8Array(1);
+    const handler = newKeyboardHandler(switches, map);
+    handler(9999, 0, KeyFlags.KeyDown);
+    assert.strictEqual(switches[0], 0x40);
+    handler(9999, 0, KeyFlags.KeyUp);
+    assert.strictEqual(switches[0], 0x00);
+  });
+
+  it('should ignore unmapped keys when no ANYKEY entry exists', function () {
+    const map = makeKeycodeMap([[Keys.A, 0, 0x01]]);
+    const switches = new Uint8Array(1);
+    const handler = newKeyboardHandler(switches, map);
+    handler(9999, 0, KeyFlags.KeyDown);
+    assert.strictEqual(switches[0], 0x00);
+  });
+
+  it('should invoke the callback function with key info', function () {
+    const map = makeKeycodeMap([[Keys.A, 0, 0x01]]);
+    const switches = new Uint8Array(1);
+    const calls = [];
+    const handler = newKeyboardHandler(switches, map, (o, key, code, flags) => {
+      calls.push([o && o.def.n, key, code, flags]);
+    });
+    handler(32, 65, KeyFlags.KeyDown | KeyFlags.Shift);
+    assert.deepStrictEqual(calls, [['Space', 32, 65, KeyFlags.KeyDown | KeyFlags.Shift]]);
+  });
+
+  it('should invoke callback for unmapped keys only with alwaysfunc', function () {
+    const map = makeKeycodeMap([[Keys.A, 0, 0x01]]);
+    const switches = new Uint8Array(1);
+    const calls = [];
+    const handler = newKeyboardHandler(switches, map, (o) => {
+      calls.push(o ? o.def.n : null);
+    }, true);
+    handler(9999, 0, KeyFlags.KeyDown);
+    assert.deepStrictEqual(calls, [null]);
+    assert.strictEqual(switches[0], 0x00);
+  });
+
+  it('should pass through to callback when no map is given', function () {
+    const switches = new Uint8Array(1);
+    const calls = [];
+    const handler = newKeyboardHandler(switches, null, (o, key, code, flags) => {
+      calls.push([o, key, code, flags]);
+    });
+    handler(65, 65, KeyFlags.KeyDown);
+    assert.deepStrictEqual(calls, [[null, 65, 65, KeyFlags.KeyDown]]);
+  });
+});
+
+describe('_setKeyboardEvents', function () {
+  it('should wire keydown and keyup handlers', function () {
+    const calls = [];
+    const canvas: any = { onkeydown: null, onkeyup: null };
+    _setKeyboardEvents(canvas, (which, keyCode, flags) => {
+      calls.push([which, keyCode, flags]);
+    });
+    canvas.onkeydown({ which: 65, keyCode: 65, shiftKey: false, ctrlKey: false, altKey: false, metaKey: false, preventDefault() { } });
+    assert.deepStrictEqual(calls[0], [65, 65, KeyFlags.KeyDown]);
+    canvas.onkeyup({ which: 65, keyCode: 65, shiftKey: true, ctrlKey: false, altKey: false, metaKey: false, preventDefault() { } });
+    assert.deepStrictEqual(calls[1], [65, 65, KeyFlags.KeyUp | KeyFlags.Shift]);
+  });
+
+  it('should pass through modifier flags', function () {
+    const calls = [];
+    const canvas: any = { onkeydown: null, onkeyup: null };
+    _setKeyboardEvents(canvas, (which, keyCode, flags) => {
+      calls.push(flags);
+    });
+    canvas.onkeydown({ which: 13, keyCode: 13, shiftKey: true, ctrlKey: true, altKey: true, metaKey: true, preventDefault() { } });
+    assert.strictEqual(calls[0], KeyFlags.KeyDown | KeyFlags.Shift | KeyFlags.Ctrl | KeyFlags.Alt | KeyFlags.Meta);
+  });
+
+  it('should preventDefault on unmodified keydown only', function () {
+    const prevented = [];
+    const canvas: any = { onkeydown: null, onkeyup: null };
+    _setKeyboardEvents(canvas, () => { });
+    canvas.onkeydown({ which: 32, keyCode: 32, shiftKey: false, ctrlKey: false, altKey: false, metaKey: false, preventDefault() { prevented.push('plain'); } });
+    canvas.onkeydown({ which: 32, keyCode: 32, shiftKey: true, ctrlKey: false, altKey: false, metaKey: false, preventDefault() { prevented.push('shift'); } });
+    assert.deepStrictEqual(prevented, ['plain']);
+  });
+});
+
+describe('padBytes', function () {
+  it('should pad at the end by default', function () {
+    const out = padBytes([1, 2, 3], 8);
+    assert.ok(out instanceof Uint8Array);
+    assert.deepStrictEqual(Array.from(out), [1, 2, 3, 0, 0, 0, 0, 0]);
+  });
+
+  it('should pad at the start when requested', function () {
+    const out = padBytes(new Uint8Array([1, 2, 3]), 8, true);
+    assert.deepStrictEqual(Array.from(out), [0, 0, 0, 0, 0, 1, 2, 3]);
+  });
+
+  it('should return unchanged data when length matches', function () {
+    const out = padBytes([0xAA, 0xBB], 2);
+    assert.deepStrictEqual(Array.from(out), [0xAA, 0xBB]);
+  });
+
+  it('should throw when data is too long', function () {
+    assert.throws(() => padBytes([1, 2, 3], 2), /Data too long, 3 > 2/);
+  });
+});
+
+describe('AddressDecoder', function () {
+  it('should decode reads from a table', function () {
+    const ram = new Uint8Array(256);
+    ram[0x10] = 0x5A;
+    const decode = newAddressDecoder([[0x0000, 0x00FF, 0, (a) => ram[a]]]);
+    assert.strictEqual(decode(0x10), 0x5A);
+    assert.strictEqual(decode(0x99), 0x00);
+  });
+
+  it('should return default value for out-of-range addresses', function () {
+    const ram = new Uint8Array(256);
+    const decode = newAddressDecoder([[0x0000, 0x00FF, 0, (a) => ram[a]]]);
+    assert.strictEqual(decode(0x1000), 0);
+  });
+
+  it('should apply address masks', function () {
+    const ram = new Uint8Array(0x800);
+    ram[0x000] = 0x11;
+    ram[0x7FF] = 0x22;
+    const decode = newAddressDecoder([[0x0000, 0x0FFF, 0x07FF, (a) => ram[a]]]);
+    assert.strictEqual(decode(0x0000), 0x11);
+    assert.strictEqual(decode(0x0800), 0x11); // 0x0800 & 0x07FF = 0x0000
+    assert.strictEqual(decode(0x0FFF), 0x22); // 0x0FFF & 0x07FF = 0x07FF
+  });
+
+  it('should support write functions and mask the result', function () {
+    const ram = new Uint8Array(0x800);
+    const decode = newAddressDecoder([[0x0000, 0x0FFF, 0x07FF,
+      (a, v) => { if (v !== undefined) ram[a] = v; return ram[a]; }]]);
+    decode(0x0801, 0x99); // writes to 0x0801 & 0x07FF = 0x0001
+    assert.strictEqual(ram[0x001], 0x99);
+    assert.strictEqual(ram[0x801], undefined);
+    assert.strictEqual(decode(0x0801), 0x99);
+  });
+
+  it('should apply a global mask before decoding', function () {
+    const ram = new Uint8Array(0x100);
+    ram[0x00] = 0x11;
+    ram[0x20] = 0x22;
+    const decode = newAddressDecoder([[0x0000, 0x00FF, 0, (a) => ram[a]]],
+      { gmask: 0x0FFF, defaultval: 0xFF });
+    assert.strictEqual(decode(0x1000), 0x11); // 0x1000 & 0x0FFF = 0x0000
+    assert.strictEqual(decode(0x0020), 0x22);
+    assert.strictEqual(decode(0x1234), 0xFF); // masked to 0x0234, out of range
+  });
+
+  it('should handle an empty table with a default value', function () {
+    const decode = newAddressDecoder([], { defaultval: 0xEE });
+    assert.strictEqual(decode(0x0000), 0xEE);
+    const decode2 = newAddressDecoder([]);
+    assert.strictEqual(decode2(0x0000), 0);
+  });
+
+  it('should be usable as a constructor directly', function () {
+    const decode = new (AddressDecoder as any)([[0x0000, 0xFFFF, 0, () => 0x42]]);
+    assert.strictEqual(decode(0x1234), 0x42);
+  });
+});
+
+describe('AnimationTimer', function () {
+  it('should invoke callback at scheduled intervals', function () {
+    let count = 0;
+    const timer = new AnimationTimer(100, () => count++); // 10ms per frame
+    timer.running = true;
+    timer.nextFrame(50); // ts > nextts(0)
+    assert.strictEqual(count, 1);
+    timer.nextFrame(60); // ts(60) < nextts(100)
+    assert.strictEqual(count, 2);
+    timer.nextFrame(150); // ts > nextts(100)
+    assert.strictEqual(count, 3); //
+    timer.running = false;
+  });
+
+  it('should not invoke callback when not running', function () {
+    let count = 0;
+    const timer = new AnimationTimer(100, () => count++);
+    timer.nextFrame(50);
+    assert.strictEqual(count, 0);
+    timer.running = true;
+    timer.nextFrame(60);
+    assert.strictEqual(count, 1);
+    timer.running = false;
+  });
+
+  it('should catch up after large gaps', function () {
+    let count = 0;
+    const timer = new AnimationTimer(100, () => count++);
+    timer.running = true;
+    timer.nextts = 500;
+    timer.nextFrame(3000); // > 1s gap: should catch up
+    assert.strictEqual(count, 1);
+    assert.strictEqual(timer.nextts, 3000);
+    timer.running = false;
+  });
+
+  it('should set frame timing properties', function () {
+    const timer = new AnimationTimer(60, () => { });
+    assert.strictEqual(timer.frameRate, 60);
+    assert.strictEqual(timer.intervalMsec, 1000 / 60);
+  });
+
+  it('should start/stop and report running state', function () {
+    const timer = new AnimationTimer(60, () => { });
+    assert.strictEqual(timer.isRunning(), false);
+    timer.start();
+    assert.strictEqual(timer.isRunning(), true);
+    timer.stop();
+    assert.strictEqual(timer.isRunning(), false);
+  });
+});
+
+describe('drawCrosshair', function () {
+  it('should no-op without setLineDash (unit testing support)', function () {
+    let called = false;
+    const ctx: any = { fillRect: () => { called = true; } };
+    drawCrosshair(ctx, 10, 20, 2);
+    assert.strictEqual(called, false);
+  });
+
+  it('should draw vertical and horizontal lines', function () {
+    const calls: any[][] = [];
+    const ctx: any = {
+      fillStyle: '', strokeStyle: '', lineWidth: 0,
+      setLineDash: (d) => calls.push(['setLineDash', String(d)]),
+      fillRect: (x, y, w, h) => calls.push(['fillRect', x, y, w, h]),
+      beginPath: () => calls.push(['beginPath']),
+      moveTo: (x, y) => calls.push(['moveTo', x, y]),
+      lineTo: (x, y) => calls.push(['lineTo', x, y]),
+      stroke: () => calls.push(['stroke']),
+    };
+    drawCrosshair(ctx, 10, 20, 2);
+    assert.ok(calls.some(c => c[0] === 'fillRect' && c[1] === 8), 'vertical bar at x-2');
+    assert.ok(calls.some(c => c[0] === 'fillRect' && c[2] === 18), 'horizontal bar at y-2');
+    assert.ok(calls.some(c => c[0] === 'moveTo' && c[1] === 10), 'vertical line at x');
+    assert.ok(calls.some(c => c[0] === 'moveTo' && c[2] === 20), 'horizontal line at y');
+    assert.ok(calls.some(c => c[0] === 'setLineDash' && c[1] === '4,4'), 'dash pattern 2*width');
+    assert.ok(calls.some(c => c[0] === 'stroke'), 'stroke called');
+  });
+});
+
+describe('getMousePos', function () {
+  const realWindow = (global as any).window;
+
+  after(function () {
+    if (realWindow === undefined) delete (global as any).window;
+    else (global as any).window = realWindow;
+  });
+
+  function stubWindow() {
+    (global as any).window = {
+      getComputedStyle: () => ({
+        borderLeftWidth: '0px', borderRightWidth: '0px',
+        borderTopWidth: '0px', borderBottomWidth: '0px',
+        paddingLeft: '0px', paddingRight: '0px',
+        paddingTop: '0px', paddingBottom: '0px',
+      })
+    };
+  }
+
+  it('should clamp out-of-bounds coordinates', function () {
+    stubWindow();
+    const canvas: any = {
+      width: 100, height: 100,
+      getBoundingClientRect: () => ({ left: 0, top: 0, width: 100, height: 100 })
+    };
+    const pos = getMousePos(canvas, { clientX: 10000, clientY: -100 });
+    assert.deepStrictEqual(pos, { x: 100, y: 0 });
+  });
+
+  it('should account for borders and padding', function () {
+    (global as any).window = {
+      getComputedStyle: () => ({
+        borderLeftWidth: '2px', borderRightWidth: '2px',
+        borderTopWidth: '2px', borderBottomWidth: '2px',
+        paddingLeft: '2px', paddingRight: '2px',
+        paddingTop: '2px', paddingBottom: '2px',
+      })
+    };
+    const canvas: any = {
+      width: 100, height: 100,
+      getBoundingClientRect: () => ({ left: 10, top: 10, width: 108, height: 108 })
+    };
+    // content origin = rect.left + border(2) + padding(2) = 14
+    let pos = getMousePos(canvas, { clientX: 14, clientY: 14 });
+    assert.deepStrictEqual(pos, { x: 0, y: 0 });
+    // content far edge
+    pos = getMousePos(canvas, { clientX: 14 + 99, clientY: 14 + 99 });
+    assert.ok(pos.x >= 99 && pos.x <= 100);
+  });
+});
+