diff --git a/CMakeLists.txt b/CMakeLists.txt
index 813c57d60..1dea1c828 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -187,6 +187,7 @@ if (NOT ${SPIRV_SKIP_EXECUTABLES})
       ${CMAKE_CURRENT_SOURCE_DIR}/test/TextToBinary.Debug.cpp
       ${CMAKE_CURRENT_SOURCE_DIR}/test/TextToBinary.Miscellaneous.cpp
       ${CMAKE_CURRENT_SOURCE_DIR}/test/TextWordGet.cpp
+      ${CMAKE_CURRENT_SOURCE_DIR}/test/UnitSPIRV.cpp
       ${CMAKE_CURRENT_SOURCE_DIR}/test/Validate.cpp
       ${CMAKE_CURRENT_SOURCE_DIR}/test/ValidateID.cpp
       ${CMAKE_CURRENT_SOURCE_DIR}/test/main.cpp)
diff --git a/test/TextToBinary.Debug.cpp b/test/TextToBinary.Debug.cpp
index 688c966fd..3a1aad40a 100644
--- a/test/TextToBinary.Debug.cpp
+++ b/test/TextToBinary.Debug.cpp
@@ -37,8 +37,11 @@
 namespace {
 
 using spvtest::MakeInstruction;
+using spvtest::MakeVector;
 using ::testing::Eq;
 
+// Test OpSource
+
 // A single test case for OpSource
 struct LanguageCase {
   const char* language_name;
@@ -74,7 +77,28 @@ TEST_P(OpSourceTest, AnyLanguage) {
 INSTANTIATE_TEST_CASE_P(TextToBinaryTestDebug, OpSourceTest,
                         ::testing::ValuesIn(kLanguageCases));
 
-// TODO(dneto): OpSourceExtension
+// Test OpSourceExtension
+
+using OpSourceExtensionTest =
+    test_fixture::TextToBinaryTestBase<::testing::TestWithParam<const char*>>;
+
+TEST_P(OpSourceExtensionTest, AnyExtension) {
+  // TODO(dneto): utf-8, quoting, escaping
+  std::string input = std::string("OpSourceExtension \"") + GetParam() + "\"";
+
+  const std::vector<uint32_t> encoded_string = MakeVector(GetParam());
+  std::vector<uint32_t> expected_instruction{
+      spvOpcodeMake(encoded_string.size() + 1, spv::OpSourceExtension)};
+  expected_instruction.insert(expected_instruction.end(),
+                              encoded_string.begin(), encoded_string.end());
+  EXPECT_THAT(CompiledInstructions(input), Eq(expected_instruction));
+}
+
+// TODO(dneto): utf-8, quoting, escaping
+INSTANTIATE_TEST_CASE_P(TextToBinaryTestDebug, OpSourceExtensionTest,
+                        ::testing::ValuesIn(std::vector<const char*>{
+                            "", "foo bar this and that"}));
+
 // TODO(dneto): OpName
 // TODO(dneto): OpMemberName
 // TODO(dneto): OpString
diff --git a/test/UnitSPIRV.cpp b/test/UnitSPIRV.cpp
new file mode 100644
index 000000000..fed239dbd
--- /dev/null
+++ b/test/UnitSPIRV.cpp
@@ -0,0 +1,46 @@
+// Copyright (c) 2015 The Khronos Group Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and/or associated documentation files (the
+// "Materials"), to deal in the Materials without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Materials, and to
+// permit persons to whom the Materials are furnished to do so, subject to
+// the following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Materials.
+//
+// MODIFICATIONS TO THIS FILE MAY MEAN IT NO LONGER ACCURATELY REFLECTS
+// KHRONOS STANDARDS. THE UNMODIFIED, NORMATIVE VERSIONS OF KHRONOS
+// SPECIFICATIONS AND HEADER INFORMATION ARE LOCATED AT
+//    https://www.khronos.org/registry/
+//
+// THE MATERIALS ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+// MATERIALS OR THE USE OR OTHER DEALINGS IN THE MATERIALS.
+
+#include "UnitSPIRV.h"
+
+#include "gmock/gmock.h"
+
+namespace {
+
+using spvtest::MakeVector;
+using ::testing::Eq;
+using Words = std::vector<uint32_t>;
+
+TEST(MakeVector, Samples) {
+  EXPECT_THAT(MakeVector(""), Eq(Words{0}));
+  EXPECT_THAT(MakeVector("a"), Eq(Words{0x0061}));
+  EXPECT_THAT(MakeVector("ab"), Eq(Words{0x006261}));
+  EXPECT_THAT(MakeVector("abc"), Eq(Words{0x00636261}));
+  EXPECT_THAT(MakeVector("abcd"), Eq(Words{0x64636261, 0x00}));
+  EXPECT_THAT(MakeVector("abcde"), Eq(Words{0x64636261, 0x0065}));
+}
+
+}  // anonymous namespace
diff --git a/test/UnitSPIRV.h b/test/UnitSPIRV.h
index 7b8a39991..370cce9c9 100644
--- a/test/UnitSPIRV.h
+++ b/test/UnitSPIRV.h
@@ -107,15 +107,38 @@ inline void PrintTo(const WordVector& words, ::std::ostream* os) {
 }
 
 // Returns a vector of words representing a single instruction with the
-// given opcode and number of operand words.
+// given opcode and operand words as a vector.
 inline std::vector<uint32_t> MakeInstruction(
-    spv::Op opcode, std::initializer_list<uint32_t> args) {
+    spv::Op opcode, std::vector<uint32_t> args) {
   std::vector<uint32_t> result{
       spvOpcodeMake(uint16_t(args.size() + 1), opcode)};
   result.insert(result.end(), args.begin(), args.end());
   return result;
 }
 
+// Encodes a string as a sequence of words, using the SPIR-V encoding.
+inline std::vector<uint32_t> MakeVector(std::string input) {
+  std::vector<uint32_t> result;
+  uint32_t word = 0;
+  size_t num_bytes = input.size();
+  // SPIR-V strings are null-terminated.  The byte_index == num_bytes
+  // case is used to push the terminating null byte.
+  for (size_t byte_index = 0; byte_index <= num_bytes; byte_index++) {
+    const auto new_byte =
+        (byte_index < num_bytes ? uint8_t(input[byte_index]) : uint8_t(0));
+    word |= (new_byte << (8 * (byte_index % sizeof(uint32_t))));
+    if (3 == (byte_index % sizeof(uint32_t))) {
+      result.push_back(word);
+      word = 0;
+    }
+  }
+  // Emit a trailing partial word.
+  if ((num_bytes+1) % sizeof(uint32_t)) {
+    result.push_back(word);
+  }
+  return result;
+}
+
 } // namespace spvtest
 
 // A type for easily creating spv_text_t values, with an implicit conversion to