message: Add tests which check that the catalogue and the key manager error messages contain the requested string.
diff: @@ -682,6 +682,8 @@ TEST_F(RegistryTest, GetKeyManagerErrorMessage) {
  auto result =
  Registry::get_key_manager<int>(AesGcmKeyManager().get_key_type());
  EXPECT_FALSE(result.ok());
  + EXPECT_THAT(result.status().error_message(),
  + HasSubstr(AesGcmKeyManager().get_key_type()));
  // Note: The C++ standard does not guarantee the next line. If some toolchain
  // update fails it, one can delete it.
  EXPECT_THAT(result.status().error_message(), HasSubstr(typeid(Aead).name()));
  @@ -695,6 +697,7 @@ TEST_F(RegistryTest, GetCatalogueErrorMessage) {
  .ok());
  auto result = Registry::get_catalogue<int>(catalogue_name);
  EXPECT_FALSE(result.ok());
  + EXPECT_THAT(result.status().error_message(), HasSubstr(catalogue_name));
  // Note: The C++ standard does not guarantee the next line. If some toolchain
  // update fails it, one can delete it.
  EXPECT_THAT(result.status().error_message(), HasSubstr(typeid(Aead).name()));
  