diff --git a/lib/n65/symbol_table.rb b/lib/n65/symbol_table.rb
index 6cc2234..af7434f 100644
--- a/lib/n65/symbol_table.rb
+++ b/lib/n65/symbol_table.rb
@@ -54,7 +54,7 @@ module N65
       scope[symbol.to_sym] = value
     end
 
-    # Separate arithmetic from scope name
+    # Separate arithmetic from symbol
     def find_arithmetic(name)
       last_name = name.split('.').last
       md = last_name.match(%r{([+\-*/])(\d+)$})
@@ -62,7 +62,7 @@ module N65
 
       unless md.nil?
         full_match, operator, argument = md.to_a
-        name.gsub!(full_match, '')
+        name = name.gsub(full_match, '')
         f = ->(value) { value.send(operator.to_sym, argument.to_i) }
       end
 
diff --git a/n65.gemspec b/n65.gemspec
index c8ca351..f5c504d 100644
--- a/n65.gemspec
+++ b/n65.gemspec
@@ -22,7 +22,6 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version = '>= 2.4.0'
 
   spec.add_development_dependency 'bundler'
-  spec.add_development_dependency 'minitest'
   spec.add_development_dependency 'rake'
   spec.add_development_dependency 'rubocop'
   spec.add_development_dependency 'rspec'
diff --git a/spec/lib/n65/symbol_table_spec.rb b/spec/lib/n65/symbol_table_spec.rb
index cf39650..bd9c831 100644
--- a/spec/lib/n65/symbol_table_spec.rb
+++ b/spec/lib/n65/symbol_table_spec.rb
@@ -203,7 +203,7 @@ RSpec.describe(N65::SymbolTable) do
         0xea,        # NOP
         0xea,        # NOP
         0xea,        # NOP
-        0x60         # RTS forward_symbol
+        0x60         # RTS
       ]
     end
     let(:emitted_rom) { assembler.emit_binary_rom.bytes[16...26] }
@@ -214,4 +214,78 @@ RSpec.describe(N65::SymbolTable) do
       expect(emitted_rom).to eq(correct_binary)
     end
   end
+
+  context 'when setting a symbols value' do
+    before do
+      subject.define_symbol('variable', 0xff)
+    end
+
+    it 'can resolve to that value' do
+      expect(subject.resolve_symbol('variable')).to eq(0xff)
+    end
+  end
+
+  context 'when performing artithmetic on a symbol' do
+    before do
+      subject.define_symbol('variable', 0x20)
+    end
+
+    it 'can perform addition on the symbol' do
+      expect(subject.resolve_symbol('variable+1')).to eq(0x21)
+    end
+
+    it 'can perform subtraction on the symbol' do
+      expect(subject.resolve_symbol('variable-16')).to eq(0x10)
+    end
+
+    it 'can perform multiplication on the symbol' do
+      expect(subject.resolve_symbol('variable*2')).to eq(0x40)
+    end
+
+    it 'can perform division on the symbol' do
+      expect(subject.resolve_symbol('variable/2')).to eq(0x10)
+    end
+  end
+
+  context 'when performing arithmetic on a scope struct' do
+    let(:assembler) { N65::Assembler.new }
+    let(:program) do
+      <<~'ASM'
+        .ines {"prog": 1, "char": 0, "mapper": 0, "mirror": 0}
+
+        .org $0020
+        .scope struct
+          .space a 1
+          .space b 1
+        .
+
+        .org $8000
+        .scope main
+          sei
+          cld
+          lda struct+1 zp
+          lda struct*2 zp
+          rts
+        .
+      ASM
+    end
+    let(:emitted_rom) { assembler.emit_binary_rom.bytes[16...23] }
+    let(:correct_binary) do
+      [
+        0x78,         #  sei
+        0xd8,         #  cld
+        0xa5,         #  lda
+        0x21,         #  $20 + 1
+        0xa5,         #  lda
+        0x40,         #  $20 * 2
+        0x60          #  rts
+      ]
+    end
+
+    before { assembler.assemble_string(program) }
+
+    it 'assembles the symbol arithmetic correctly' do
+      expect(emitted_rom).to eq(correct_binary)
+    end
+  end
 end
diff --git a/test/test_arithmetic_symbols.rb b/test/test_arithmetic_symbols.rb
deleted file mode 100644
index d30eaea..0000000
--- a/test/test_arithmetic_symbols.rb
+++ /dev/null
@@ -1,69 +0,0 @@
-gem 'minitest'
-require 'minitest/autorun'
-require 'minitest/unit'
-require_relative '../lib/n65'
-
-class TestArithmeticSymbols < MiniTest::Test
-  include N65
-
-  def test_identify_plain_symbol
-    re = Regexp.new(Regexes::Sym)
-    assert_match(re, 'dog')
-    assert_match(re, 'animal.dog')
-    assert_match(re, 'global.animal.dog')
-  end
-
-  def test_symbol_values
-    st = SymbolTable.new
-    st.define_symbol('variable', 0xff)
-    assert_equal(0xff, st.resolve_symbol('variable'))
-  end
-
-  def test_perform_symbolic_arithmetic
-    st = SymbolTable.new
-    st.define_symbol('variable', 0x20)
-    assert_equal(0x21, st.resolve_symbol('variable+1'))
-    assert_equal(0x40, st.resolve_symbol('variable*2'))
-  end
-
-  def test_symbol_addition
-    program = <<-ASM
-    .ines {"prog": 1, "char": 0, "mapper": 0, "mirror": 0}
-
-    .org $0020
-    .scope struct
-      .space a 1
-      .space b 1
-    .
-
-    .org $8000
-    .scope main
-      sei
-      cld
-      lda struct+1 zp
-      lda struct*2 zp
-      rts
-    .
-    ASM
-
-    assembler = Assembler.new
-    program.split(/\n/).each do |line|
-      assembler.assemble_one_line(line)
-    end
-    assembler.fulfill_promises
-
-    binary = assembler.emit_binary_rom[16...23].split(//).map(&:ord)
-
-    ##  So yay, arithmetic on symbols works now :)
-    correct = [
-      0x78,         #  sei
-      0xd8,         #  cld
-      0xa5,         #  lda
-      0x21,         #  $20 + 1
-      0xa5,         #  lda
-      0x40,         #  $20 * 2
-      0x60          #  rts
-    ]
-    assert_equal(binary, correct)
-  end
-end