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<div id="projectname">GRPC C++
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 <span id="projectnumber">1.22.0</span>
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<div class="title">How to write unit tests for gRPC C client. </div> </div>
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<div class="contents">
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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>
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<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>
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<p>For instance, consider an EchoService like this:</p>
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<div class="fragment"><div class="line">service EchoTestService {</div><div class="line"> rpc Echo(EchoRequest) returns (EchoResponse);</div><div class="line"> rpc BidiStream(stream EchoRequest) returns (stream EchoResponse);</div><div class="line">}</div></div><!-- fragment --><p>The code generated would look something like this:</p>
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<div class="fragment"><div class="line"><span class="keyword">class </span>EchoTestService final {</div><div class="line"> <span class="keyword">public</span>:</div><div class="line"> <span class="keyword">class </span>StubInterface {</div><div class="line"> <a class="code" href="namespacegrpc_1_1protobuf_1_1util.html#a717f1a5db6c98d3f27340afd6f28bf7e">virtual ::grpc::Status</a> Echo(::<a class="code" href="classgrpc__impl_1_1_client_context.html">grpc::ClientContext</a>* context, const ::grpc::testing::EchoRequest& request, ::grpc::testing::EchoResponse* response) = 0;</div><div class="line"> …</div><div class="line"> std::unique_ptr< ::grpc::ClientReaderWriterInterface< ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse>> BidiStream(::<a class="code" href="classgrpc__impl_1_1_client_context.html">grpc::ClientContext</a>* context) {</div><div class="line"> <span class="keywordflow">return</span> std::unique_ptr< ::grpc::ClientReaderWriterInterface< ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse>>(BidiStreamRaw(context));</div><div class="line"> }</div><div class="line"> …</div><div class="line"> <span class="keyword">private</span>:</div><div class="line"> virtual ::grpc::ClientReaderWriterInterface< ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse>* BidiStreamRaw(::<a class="code" href="classgrpc__impl_1_1_client_context.html">grpc::ClientContext</a>* context) = 0;</div><div class="line"> …</div><div class="line"> } <span class="comment">// End StubInterface</span></div><div class="line">…</div><div class="line">} <span class="comment">// End EchoTestService</span></div></div><!-- fragment --><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>
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<p>A mock for this StubInterface will look like this:</p>
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<div class="fragment"><div class="line"><span class="keyword">class </span>MockEchoTestServiceStub : <span class="keyword">public</span> EchoTestService::StubInterface {</div><div class="line"> <span class="keyword">public</span>:</div><div class="line"> MOCK_METHOD3(Echo, ::<a class="code" href="classgrpc_1_1_status.html">grpc::Status</a>(::<a class="code" href="classgrpc__impl_1_1_client_context.html">grpc::ClientContext</a>* context, const ::grpc::testing::EchoRequest& request, ::grpc::testing::EchoResponse* response));</div><div class="line"> MOCK_METHOD1(BidiStreamRaw, ::<a class="code" href="classgrpc_1_1_client_reader_writer_interface.html">grpc::ClientReaderWriterInterface< ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse></a>*(::<a class="code" href="classgrpc__impl_1_1_client_context.html">grpc::ClientContext</a>* context));</div><div class="line">};</div></div><!-- fragment --><p><b>Generating mock code:</b></p>
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<p>Such a mock can be auto-generated by:</p>
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<ol type="1">
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<li>Setting flag(generate_mock_code=true) on grpc plugin for protoc, or</li>
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</ol>
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<ol type="1">
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<li>Setting an attribute(generate_mocks) in your bazel rule.</li>
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</ol>
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<p>Protoc plugin flag:</p>
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<div class="fragment"><div class="line">protoc -I . --grpc_out=generate_mock_code=true:. --plugin=protoc-gen-grpc=`which grpc_cpp_plugin` echo.proto</div></div><!-- fragment --><p>Bazel rule:</p>
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<div class="fragment"><div class="line">grpc_proto_library(</div><div class="line"> name = <span class="stringliteral">"echo_proto"</span>,</div><div class="line"> srcs = [<span class="stringliteral">"echo.proto"</span>],</div><div class="line"> generate_mocks = <span class="keyword">True</span>,</div><div class="line">)</div></div><!-- fragment --><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>
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<p>This header file can then be included in test files along with a gmock dependency.</p>
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<p><b>Writing tests with mocked Stub.</b></p>
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<p>Consider the following client a user might have:</p>
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<div class="fragment"><div class="line"><span class="keyword">class </span>FakeClient {</div><div class="line"> <span class="keyword">public</span>:</div><div class="line"> <span class="keyword">explicit</span> FakeClient(EchoTestService::StubInterface* stub) : stub_(stub) {}</div><div class="line"></div><div class="line"> <span class="keywordtype">void</span> DoEcho() {</div><div class="line"> <a class="code" href="namespacegrpc.html#a35a61e2e00942ae1f40dda77413425ac">ClientContext</a> context;</div><div class="line"> EchoRequest request;</div><div class="line"> EchoResponse response;</div><div class="line"> request.set_message(<span class="stringliteral">"hello world"</span>);</div><div class="line"> <a class="code" href="namespacegrpc_1_1protobuf_1_1util.html#a717f1a5db6c98d3f27340afd6f28bf7e">Status</a> s = stub_->Echo(&context, request, &response);</div><div class="line"> EXPECT_EQ(request.message(), response.message());</div><div class="line"> EXPECT_TRUE(s.ok());</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="keywordtype">void</span> DoBidiStream() {</div><div class="line"> EchoRequest request;</div><div class="line"> EchoResponse response;</div><div class="line"> <a class="code" href="namespacegrpc.html#a35a61e2e00942ae1f40dda77413425ac">ClientContext</a> context;</div><div class="line"> <a class="code" href="namespacegrpc.html#ab04a87625da3bf85cdaf5e7856b00203">grpc::string</a> msg(<span class="stringliteral">"hello"</span>);</div><div class="line"></div><div class="line"> std::unique_ptr<ClientReaderWriterInterface<EchoRequest, EchoResponse>></div><div class="line"> stream = stub_->BidiStream(&context);</div><div class="line"></div><div class="line"> request.set_message(msg <span class="stringliteral">"0"</span>);</div><div class="line"> EXPECT_TRUE(stream->Write(request));</div><div class="line"> EXPECT_TRUE(stream->Read(&response));</div><div class="line"> EXPECT_EQ(response.message(), request.message());</div><div class="line"></div><div class="line"> request.set_message(msg <span class="stringliteral">"1"</span>);</div><div class="line"> EXPECT_TRUE(stream->Write(request));</div><div class="line"> EXPECT_TRUE(stream->Read(&response));</div><div class="line"> EXPECT_EQ(response.message(), request.message());</div><div class="line"></div><div class="line"> request.set_message(msg <span class="stringliteral">"2"</span>);</div><div class="line"> EXPECT_TRUE(stream->Write(request));</div><div class="line"> EXPECT_TRUE(stream->Read(&response));</div><div class="line"> EXPECT_EQ(response.message(), request.message());</div><div class="line"></div><div class="line"> stream->WritesDone();</div><div class="line"> EXPECT_FALSE(stream->Read(&response));</div><div class="line"></div><div class="line"> <a class="code" href="namespacegrpc_1_1protobuf_1_1util.html#a717f1a5db6c98d3f27340afd6f28bf7e">Status</a> s = stream->Finish();</div><div class="line"> EXPECT_TRUE(s.ok());</div><div class="line"> }</div><div class="line"></div><div class="line"> <span class="keywordtype">void</span> ResetStub(EchoTestService::StubInterface* stub) { stub_ = stub; }</div><div class="line"></div><div class="line"> <span class="keyword">private</span>:</div><div class="line"> EchoTestService::StubInterface* stub_;</div><div class="line">};</div></div><!-- fragment --><p>A test could initialize this FakeClient with a mocked stub having set expectations on it:</p>
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<p>Unary RPC:</p>
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<div class="fragment"><div class="line">MockEchoTestServiceStub stub;</div><div class="line">EchoResponse resp;</div><div class="line">resp.set_message(<span class="stringliteral">"hello world"</span>);</div><div class="line">Expect_CALL(stub, Echo(_,_,_)).Times(Atleast(1)).WillOnce(DoAll(SetArgPointee<2>(resp), Return(<a class="code" href="namespacegrpc.html#aff1730578c90160528f6a8d67ef5c43baf6f3078af147d683afc70e09695c7a65">Status::OK</a>)));</div><div class="line">FakeClient client(stub);</div><div class="line">client.DoEcho();</div></div><!-- fragment --><p>Streaming RPC:</p>
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<div class="fragment"><div class="line">ACTION_P(copy, msg) {</div><div class="line"> arg0->set_message(msg->message());</div><div class="line">}</div><div class="line"></div><div class="line"></div><div class="line"><span class="keyword">auto</span> rw = <span class="keyword">new</span> MockClientReaderWriter<EchoRequest, EchoResponse>();</div><div class="line">EchoRequest msg;</div><div class="line">EXPECT_CALL(*rw, Write(_, _)).Times(3).WillRepeatedly(DoAll(SaveArg<0>(&msg), Return(<span class="keyword">true</span>)));</div><div class="line">EXPECT_CALL(*rw, Read(_)).</div><div class="line"> WillOnce(DoAll(WithArg<0>(copy(&msg)), Return(<span class="keyword">true</span>))).</div><div class="line"> WillOnce(DoAll(WithArg<0>(copy(&msg)), Return(<span class="keyword">true</span>))).</div><div class="line"> WillOnce(DoAll(WithArg<0>(copy(&msg)), Return(<span class="keyword">true</span>))).</div><div class="line"> WillOnce(Return(<span class="keyword">false</span>));</div><div class="line"></div><div class="line">MockEchoTestServiceStub stub;</div><div class="line">EXPECT_CALL(stub, BidiStreamRaw(_)).Times(AtLeast(1)).WillOnce(Return(rw));</div><div class="line"></div><div class="line">FakeClient client(stub);</div><div class="line">client.DoBidiStream();</div></div><!-- fragment --> </div></div><!-- contents -->
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