How to test and mock a GRPC service written in Java using Mockito

Question

The protobuf definition is as follows:

syntax = "proto3";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

I need to use Mockito along with JUnit testing.

Answer 1

The idea is to stub the response and stream observer.

@Test
public void shouldTestGreeterService() throws Exception {

    Greeter service = new Greeter();

    HelloRequest req = HelloRequest.newBuilder()
            .setName("hello")
            .build();

    StreamObserver<HelloRequest> observer = mock(StreamObserver.class);

    service.sayHello(req, observer);

    verify(observer, times(1)).onCompleted();

    ArgumentCaptor<HelloReply> captor = ArgumentCaptor.forClass(HelloReply.class);

    verify(observer, times(1)).onNext(captor.capture());

    HelloReply response = captor.getValue();

    assertThat(response.getStatus(), is(true));
}