Add unit tests for StringValue and Value.

Add unit test framework to CMakeLists.txt.
Fix a couple of bugs found by unit tests.

Change-Id: I2092a7f0570fae0f19f9e083c4837ccefcc4ca1a

test/unit/test_StringValue.cpp

@@ -0,0 +1,52 @@
+#include "Value.h"
+
+#include "gtest/gtest.h"
+
+namespace ntimpl {
+
+class StringValueTest : public ::testing::Test {
+ public:
+  NT_String& ToNT(StringValue& v) { return v; }
+};
+
+TEST_F(StringValueTest, ConstructEmpty) {
+  StringValue v;
+  ASSERT_EQ(ToNT(v).str, nullptr);
+  ASSERT_EQ(ToNT(v).len, 0u);
+}
+
+TEST_F(StringValueTest, ConstructStringRef) {
+  StringValue v("hello");
+  ASSERT_EQ(llvm::StringRef(v), "hello");
+  ASSERT_EQ(ToNT(v).str, llvm::StringRef("hello"));
+  ASSERT_EQ(ToNT(v).len, 5u);
+}
+
+TEST_F(StringValueTest, ConstructMove) {
+  StringValue v("hello");
+  char* orig = ToNT(v).str;
+  ASSERT_NE(orig, nullptr);
+  ASSERT_EQ(ToNT(v).len, 5u);
+  StringValue v2(std::move(v));
+  ASSERT_EQ(ToNT(v).str, nullptr);
+  ASSERT_EQ(ToNT(v).len, 0u);
+  ASSERT_EQ(ToNT(v2).str, orig);
+  ASSERT_EQ(ToNT(v2).len, 5u);
+}
+
+TEST_F(StringValueTest, AssignMove) {
+  StringValue v("hello");
+  char* orig = ToNT(v).str;
+  ASSERT_NE(orig, nullptr);
+  ASSERT_EQ(ToNT(v).len, 5u);
+  StringValue v2("goodbye");
+  ASSERT_NE(ToNT(v2).str, nullptr);
+  ASSERT_EQ(ToNT(v2).len, 7u);
+  v2 = std::move(v);
+  ASSERT_EQ(ToNT(v).str, nullptr);
+  ASSERT_EQ(ToNT(v).len, 0u);
+  ASSERT_EQ(ToNT(v2).str, orig);
+  ASSERT_EQ(ToNT(v2).len, 5u);
+}
+
+}  // namespace ntimpl