add showcase tests

Author: JoeWang1127

showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/IdentityClientTest.java

@@ -35,6 +35,7 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.UUID;
+import java.util.stream.Stream;
 import javax.annotation.Generated;
 import org.junit.After;
 import org.junit.AfterClass;
@@ -442,6 +443,41 @@ public void listUsersTest() throws Exception {
             GaxGrpcProperties.getDefaultApiClientHeaderPattern()));
   }
 
+  @Test
+  public void listUsersTest2() throws Exception {
+    User responsesElement = User.newBuilder().build();
+    ListUsersResponse expectedResponse =
+        ListUsersResponse.newBuilder()
+            .setNextPageToken("")
+            .addAllUsers(Arrays.asList(responsesElement))
+            .build();
+    mockIdentity.addResponse(expectedResponse);
+
+    ListUsersRequest request =
+        ListUsersRequest.newBuilder()
+            .setPageSize(883849137)
+            .setPageToken("pageToken873572522")
+            .build();
+
+    ListUsersPagedResponse pagedListResponse = client.listUsers(request);
+
+    Stream<User> resources = pagedListResponse.getPage().streamAll();
+
+    Assert.assertEquals(1, resources.count());
+    Assert.assertEquals(responsesElement, resources.findFirst().get());
+
+    List<AbstractMessage> actualRequests = mockIdentity.getRequests();
+    Assert.assertEquals(1, actualRequests.size());
+    ListUsersRequest actualRequest = ((ListUsersRequest) actualRequests.get(0));
+
+    Assert.assertEquals(request.getPageSize(), actualRequest.getPageSize());
+    Assert.assertEquals(request.getPageToken(), actualRequest.getPageToken());
+    Assert.assertTrue(
+        channelProvider.isHeaderSent(
+            ApiClientHeaderProvider.getDefaultApiClientHeaderKey(),
+            GaxGrpcProperties.getDefaultApiClientHeaderPattern()));
+  }
+
   @Test
   public void listUsersExceptionTest() throws Exception {
     StatusRuntimeException exception = new StatusRuntimeException(io.grpc.Status.INVALID_ARGUMENT);