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<div class="title">How to write unit tests for gRPC C client. </div>  </div>
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<div class="textblock"><p>tl;dr: <a href="https://github.com/grpc/grpc/blob/master/test/cpp/end2end/mock_test.cc">Example code</a>.</p>
<p>To unit-test client-side logic via the synchronous API, gRPC provides a mocked Stub based on googletest(googlemock) that can be programmed upon and easily incorporated in the test code.</p>
<p>For instance, consider an EchoService like this:</p>
<p>```proto service EchoTestService { rpc Echo(EchoRequest) returns (EchoResponse); rpc BidiStream(stream EchoRequest) returns (stream EchoResponse); } ```</p>
<p>The code generated would look something like this:</p>
<p>```c class EchoTestService final { public: class StubInterface { virtual ::grpc::Status Echo(::grpc::ClientContext* context, const ::grpc::testing::EchoRequest&amp; request, ::grpc::testing::EchoResponse* response) = 0; … std::unique_ptr&lt; ::grpc::ClientReaderWriterInterface&lt; ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse&gt;&gt; BidiStream(::grpc::ClientContext* context) { return std::unique_ptr&lt; ::grpc::ClientReaderWriterInterface&lt; ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse&gt;&gt;(BidiStreamRaw(context)); } … private: virtual ::grpc::ClientReaderWriterInterface&lt; ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse&gt;* BidiStreamRaw(::grpc::ClientContext* context) = 0; … } // End StubInterface … } // End EchoTestService ```</p>
<p>If we mock the StubInterface and set expectations on the pure-virtual methods we can test client-side logic without having to make any rpcs.</p>
<p>A mock for this StubInterface will look like this:</p>
<p>```c class MockEchoTestServiceStub : public EchoTestService::StubInterface { public: MOCK_METHOD3(Echo, ::grpc::Status(::grpc::ClientContext* context, const ::grpc::testing::EchoRequest&amp; request, ::grpc::testing::EchoResponse* response)); MOCK_METHOD1(BidiStreamRaw, ::grpc::ClientReaderWriterInterface&lt; ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse&gt;*(::grpc::ClientContext* context)); }; ```</p>
<p><b>Generating mock code:</b></p>
<p>Such a mock can be auto-generated by:</p>
<ol type="1">
<li>Setting flag(generate_mock_code=true) on grpc plugin for protoc, or</li>
</ol>
<ol type="1">
<li>Setting an attribute(generate_mock) in your bazel rule.</li>
</ol>
<p>Protoc plugin flag:</p>
<p>``<code>sh protoc -I . --grpc_out=generate_mock_code=true:. --plugin=protoc-gen-grpc=</code>which grpc_cpp_plugin<code>echo.proto </code>``</p>
<p>Bazel rule:</p>
<p>```py grpc_proto_library( name = "echo_proto", srcs = ["echo.proto"], generate_mock = True, ) ```</p>
<p>By adding such a flag now a header file <code>echo_mock.grpc.pb.h</code> containing the mocked stub will also be generated.</p>
<p>This header file can then be included in test files along with a gmock dependency.</p>
<p><b>Writing tests with mocked Stub.</b></p>
<p>Consider the following client a user might have:</p>
<p>```c class FakeClient { public: explicit FakeClient(EchoTestService::StubInterface* stub) : stub_(stub) {}</p>
<p>void DoEcho() { ClientContext context; EchoRequest request; EchoResponse response; request.set_message("hello world"); Status s = stub_-&gt;Echo(&amp;context, request, &amp;response); EXPECT_EQ(request.message(), response.message()); EXPECT_TRUE(s.ok()); }</p>
<p>void DoBidiStream() { EchoRequest request; EchoResponse response; ClientContext context; grpc::string msg("hello");</p>
<p>std::unique_ptr&lt;ClientReaderWriterInterface&lt;EchoRequest, EchoResponse&gt;&gt; stream = stub_-&gt;BidiStream(&amp;context);</p>
<p>request.set_message(msg "0"); EXPECT_TRUE(stream-&gt;Write(request)); EXPECT_TRUE(stream-&gt;Read(&amp;response)); EXPECT_EQ(response.message(), request.message());</p>
<p>request.set_message(msg "1"); EXPECT_TRUE(stream-&gt;Write(request)); EXPECT_TRUE(stream-&gt;Read(&amp;response)); EXPECT_EQ(response.message(), request.message());</p>
<p>request.set_message(msg "2"); EXPECT_TRUE(stream-&gt;Write(request)); EXPECT_TRUE(stream-&gt;Read(&amp;response)); EXPECT_EQ(response.message(), request.message());</p>
<p>stream-&gt;WritesDone(); EXPECT_FALSE(stream-&gt;Read(&amp;response));</p>
<p>Status s = stream-&gt;Finish(); EXPECT_TRUE(s.ok()); }</p>
<p>void ResetStub(EchoTestService::StubInterface* stub) { stub_ = stub; }</p>
<p>private: EchoTestService::StubInterface* stub_; }; ```</p>
<p>A test could initialize this FakeClient with a mocked stub having set expectations on it:</p>
<p>Unary RPC:</p>
<p>```c MockEchoTestServiceStub stub; EchoResponse resp; resp.set_message("hello world"); Expect_CALL(stub, Echo(_,_,_)).Times(Atleast(1)).WillOnce(DoAll(SetArgPointee&lt;2&gt;(resp), Return(Status::OK))); FakeClient client(stub); client.DoEcho(); ```</p>
<p>Streaming RPC:</p>
<p>```c ACTION_P(copy, msg) { arg0-&gt;set_message(msg-&gt;message()); }</p>
<p>auto rw = new MockClientReaderWriter&lt;EchoRequest, EchoResponse&gt;(); EchoRequest msg; EXPECT_CALL(*rw, Write(_, _)).Times(3).WillRepeatedly(DoAll(SaveArg&lt;0&gt;(&amp;msg), Return(true))); EXPECT_CALL(*rw, Read(_)). WillOnce(DoAll(WithArg&lt;0&gt;(copy(&amp;msg)), Return(true))). WillOnce(DoAll(WithArg&lt;0&gt;(copy(&amp;msg)), Return(true))). WillOnce(DoAll(WithArg&lt;0&gt;(copy(&amp;msg)), Return(true))). WillOnce(Return(false));</p>
<p>MockEchoTestServiceStub stub; EXPECT_CALL(stub, BidiStreamRaw(_)).Times(AtLeast(1)).WillOnce(Return(rw));</p>
<p>FakeClient client(stub); client.DoBidiStream(); ``` </p>
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