diff --git a/unittests/CMakeLists.txt b/unittests/CMakeLists.txt
index 19c2d24534b..a1272edcc97 100644
--- a/unittests/CMakeLists.txt
+++ b/unittests/CMakeLists.txt
@@ -22,5 +22,6 @@ add_subdirectory(LineEditor)
 add_subdirectory(Linker)
 add_subdirectory(MC)
 add_subdirectory(Option)
+add_subdirectory(ProfileData)
 add_subdirectory(Support)
 add_subdirectory(Transforms)
diff --git a/unittests/Makefile b/unittests/Makefile
index 603e7d58f8c..fefef0748b9 100644
--- a/unittests/Makefile
+++ b/unittests/Makefile
@@ -10,7 +10,7 @@
 LEVEL = ..
 
 PARALLEL_DIRS = ADT Analysis Bitcode CodeGen DebugInfo ExecutionEngine IR \
-		LineEditor Linker MC Option Support Transforms
+		LineEditor Linker MC Option ProfileData Support Transforms
 
 include $(LEVEL)/Makefile.config
 include $(LLVM_SRC_ROOT)/unittests/Makefile.unittest
diff --git a/unittests/ProfileData/CMakeLists.txt b/unittests/ProfileData/CMakeLists.txt
new file mode 100644
index 00000000000..3251ff41502
--- /dev/null
+++ b/unittests/ProfileData/CMakeLists.txt
@@ -0,0 +1,9 @@
+set(LLVM_LINK_COMPONENTS
+  Core
+  ProfileData
+  Support
+  )
+
+add_llvm_unittest(ProfileDataTests
+  CoverageMappingTest.cpp
+  )
diff --git a/unittests/ProfileData/CoverageMappingTest.cpp b/unittests/ProfileData/CoverageMappingTest.cpp
new file mode 100644
index 00000000000..5477f814300
--- /dev/null
+++ b/unittests/ProfileData/CoverageMappingTest.cpp
@@ -0,0 +1,112 @@
+//===- unittest/ProfileData/CoverageMappingTest.cpp -------------------------=//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ProfileData/CoverageMapping.h"
+#include "llvm/ProfileData/CoverageMappingReader.h"
+#include "llvm/ProfileData/CoverageMappingWriter.h"
+#include "llvm/Support/raw_ostream.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace coverage;
+
+namespace llvm {
+namespace coverage {
+void PrintTo(const Counter &C, ::std::ostream *os) {
+  if (C.isZero())
+    *os << "Zero";
+  else if (C.isExpression())
+    *os << "Expression " << C.getExpressionID();
+  else
+    *os << "Counter " << C.getCounterID();
+}
+}
+}
+
+namespace {
+
+static std::string writeCoverage(MutableArrayRef<CounterMappingRegion> Regions,
+                                 int NumFiles) {
+  SmallVector<unsigned, 8> FileIDs;
+  for (int I = 0; I < NumFiles; ++I)
+    FileIDs.push_back(I);
+
+  std::string Coverage;
+  llvm::raw_string_ostream OS(Coverage);
+  CoverageMappingWriter(FileIDs, None, Regions).write(OS);
+  OS.flush();
+
+  return Coverage;
+}
+
+static std::vector<CounterMappingRegion>
+readCoverageRegions(std::string Coverage, int NumFiles) {
+  SmallVector<std::string, 8> Filenames;
+  SmallVector<StringRef, 8> FilenameRefs;
+  for (int I = 0; I < NumFiles; ++I) {
+    Filenames.push_back("file" + std::to_string(I));
+    FilenameRefs.push_back(Filenames.back());
+  }
+
+  std::vector<StringRef> FuncFiles;
+  std::vector<CounterExpression> Expressions;
+  std::vector<CounterMappingRegion> Regions;
+  RawCoverageMappingReader Reader(Coverage, FilenameRefs, FuncFiles,
+                                  Expressions, Regions);
+  if (Reader.read())
+    // ASSERT doesn't work here, we'll just return an empty vector.
+    Regions.clear();
+  return Regions;
+}
+
+TEST(CoverageMappingTest, basic_write_read) {
+  int NumFiles = 2;
+  CounterMappingRegion InputRegions[] = {
+      CounterMappingRegion::makeRegion(Counter::getCounter(0), 0, 1, 1, 1, 1),
+      CounterMappingRegion::makeRegion(Counter::getCounter(1), 0, 2, 1, 2, 2),
+      CounterMappingRegion::makeRegion(Counter::getZero(), 0, 3, 1, 3, 4),
+      CounterMappingRegion::makeRegion(Counter::getCounter(2), 0, 4, 1, 4, 8),
+      CounterMappingRegion::makeRegion(Counter::getCounter(3), 1, 1, 2, 3, 4),
+  };
+  std::string Coverage = writeCoverage(InputRegions, NumFiles);
+  std::vector<CounterMappingRegion> OutputRegions =
+      readCoverageRegions(Coverage, NumFiles);
+  ASSERT_FALSE(OutputRegions.empty());
+
+  size_t N = makeArrayRef(InputRegions).size();
+  ASSERT_EQ(N, OutputRegions.size());
+  for (size_t I = 0; I < N; ++I) {
+    ASSERT_EQ(InputRegions[I].Count, OutputRegions[I].Count);
+    ASSERT_EQ(InputRegions[I].FileID, OutputRegions[I].FileID);
+    ASSERT_EQ(InputRegions[I].startLoc(), OutputRegions[I].startLoc());
+    ASSERT_EQ(InputRegions[I].endLoc(), OutputRegions[I].endLoc());
+    ASSERT_EQ(InputRegions[I].Kind, OutputRegions[I].Kind);
+  }
+}
+
+TEST(CoverageMappingTest, expansion_gets_first_counter) {
+  int NumFiles = 2;
+  CounterMappingRegion InputRegions[] = {
+      CounterMappingRegion::makeRegion(Counter::getCounter(1), 0, 10, 1, 10, 2),
+      // This starts earlier in file 0, so the expansion should get its counter.
+      CounterMappingRegion::makeRegion(Counter::getCounter(2), 0, 1, 1, 20, 1),
+      CounterMappingRegion::makeExpansion(1, 0, 3, 3, 3, 3),
+  };
+  std::string Coverage = writeCoverage(InputRegions, NumFiles);
+  std::vector<CounterMappingRegion> OutputRegions =
+      readCoverageRegions(Coverage, NumFiles);
+  ASSERT_FALSE(OutputRegions.empty());
+
+  ASSERT_EQ(CounterMappingRegion::ExpansionRegion, OutputRegions[2].Kind);
+  ASSERT_EQ(Counter::getCounter(2), OutputRegions[2].Count);
+  ASSERT_EQ(3U, OutputRegions[2].LineStart);
+}
+
+
+} // end anonymous namespace
diff --git a/unittests/ProfileData/Makefile b/unittests/ProfileData/Makefile
new file mode 100644
index 00000000000..d017c15c00a
--- /dev/null
+++ b/unittests/ProfileData/Makefile
@@ -0,0 +1,15 @@
+##===- unittests/ProfileData/Makefile ----------------------*- Makefile -*-===##
+#
+#                     The LLVM Compiler Infrastructure
+#
+# This file is distributed under the University of Illinois Open Source
+# License. See LICENSE.TXT for details.
+#
+##===----------------------------------------------------------------------===##
+
+LEVEL = ../..
+TESTNAME = ProfileData
+LINK_COMPONENTS := ProfileData Core Support
+
+include $(LEVEL)/Makefile.config
+include $(LLVM_SRC_ROOT)/unittests/Makefile.unittest