skip test when impersonation sa not defined

Author: scotthart

google/cloud/pubsub/integration_tests/subscriber_integration_test.cc

@@ -58,10 +58,6 @@ using ::testing::ElementsAreArray;
 using ::testing::IsEmpty;
 using ::testing::NotNull;
 
-bool UsingEmulator() {
-  return google::cloud::internal::GetEnv("PUBSUB_EMULATOR_HOST").has_value();
-}
-
 class SubscriberIntegrationTest
     : public ::google::cloud::testing_util::IntegrationTest {
  protected:
@@ -356,12 +352,11 @@ TEST_F(SubscriberIntegrationTest, PublishPullAck) {
 }
 
 TEST_F(SubscriberIntegrationTest, PublishPullAckWithImpersonatedCredentials) {
-  if (UsingEmulator()) GTEST_SKIP();
   std::string iam_service_account =
       google::cloud::internal::GetEnv(
           "GOOGLE_CLOUD_CPP_PUBSUB_TEST_IMPERSONATED_SERVICE_ACCOUNT")
           .value_or("");
-  ASSERT_THAT(iam_service_account, Not(IsEmpty()));
+  if (iam_service_account.empty()) GTEST_SKIP();
   auto google_default_credentials = MakeGoogleDefaultCredentials();
   auto options = Options{}.set<UnifiedCredentialsOption>(
       MakeImpersonateServiceAccountCredentials(google_default_credentials,