Add unittest for EmbeddedSpec for non-existing mappings

this uses internal functions from GoogleTests
to capture the stderr message but according to the documentation
it should be fine to use them:
// All macros ending with _ and symbols defined in an
// internal namespace are subject to change without notice.  Code
// outside Google Test MUST NOT USE THEM DIRECTLY.  Macros that don't
// end with _ are part of Google Test's public API and can be used by
// code outside Google Test.
see https://github.com/google/googletest/blob/main/googletest/include/gtest/internal/gtest-port.h

Signed-off-by: Bi0T1N <Bi0T1N@users.noreply.github.com>

src/SDF_TEST.cc

@@ -559,6 +559,26 @@ TEST(SDF, EmbeddedSpec)
   EXPECT_NE(result.find("name=\"version\" type=\"string\""), std::string::npos);
 }
 
+TEST(SDF, EmbeddedSpecNonExistent)
+{
+  std::string result;
+  std::string output;
+
+  testing::internal::CaptureStderr();
+  result = sdf::SDF::EmbeddedSpec("unavailable.sdf", false);
+  output = testing::internal::GetCapturedStderr();
+  EXPECT_NE(output.find("Unable to find SDF filename"), std::string::npos);
+  EXPECT_NE(output.find("with version"), std::string::npos);
+  EXPECT_TRUE(result.empty());
+
+  output = "";
+  testing::internal::CaptureStderr();
+  result = sdf::SDF::EmbeddedSpec("unavailable.sdf", true);
+  output = testing::internal::GetCapturedStderr();
+  EXPECT_TRUE(output.empty());
+  EXPECT_TRUE(result.empty());
+}
+
 /////////////////////////////////////////////////
 TEST(SDF, FilePath)
 {