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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>
<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>
<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">    virtual ::grpc::Status Echo(::grpc::ClientContext* context, const ::grpc::testing::EchoRequest&amp; request, ::grpc::testing::EchoResponse* response) = 0;</div><div class="line">  …</div><div class="line">    std::unique_ptr&lt; ::grpc::ClientReaderWriterInterface&lt; ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse&gt;&gt; BidiStream(::grpc::ClientContext* context) {</div><div class="line">      <span class="keywordflow">return</span> std::unique_ptr&lt; ::grpc::ClientReaderWriterInterface&lt; ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse&gt;&gt;(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&lt; ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse&gt;* BidiStreamRaw(::grpc::ClientContext* 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>
<p>A mock for this StubInterface will look like this:</p>
<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, ::grpc::Status(::grpc::ClientContext* context, const ::grpc::testing::EchoRequest&amp; request, ::grpc::testing::EchoResponse* response));</div><div class="line">  MOCK_METHOD1(BidiStreamRaw, ::grpc::ClientReaderWriterInterface&lt; ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse&gt;*(::grpc::ClientContext* context));</div><div class="line">};</div></div><!-- fragment --><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_mocks) in your bazel rule.</li>
</ol>
<p>Protoc plugin flag:</p>
<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>
<div class="fragment"><div class="line">grpc_proto_library(</div><div class="line">  name = <span class="stringliteral">&quot;echo_proto&quot;</span>,</div><div class="line">  srcs = [<span class="stringliteral">&quot;echo.proto&quot;</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>
<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>
<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">    ClientContext context;</div><div class="line">    EchoRequest request;</div><div class="line">    EchoResponse response;</div><div class="line">    request.set_message(<span class="stringliteral">&quot;hello world&quot;</span>);</div><div class="line">    Status s = stub_-&gt;Echo(&amp;context, request, &amp;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">    ClientContext context;</div><div class="line">    grpc::string msg(<span class="stringliteral">&quot;hello&quot;</span>);</div><div class="line"></div><div class="line">    std::unique_ptr&lt;ClientReaderWriterInterface&lt;EchoRequest, EchoResponse&gt;&gt;</div><div class="line">        stream = stub_-&gt;BidiStream(&amp;context);</div><div class="line"></div><div class="line">    request.set_message(msg  <span class="stringliteral">&quot;0&quot;</span>);</div><div class="line">    EXPECT_TRUE(stream-&gt;Write(request));</div><div class="line">    EXPECT_TRUE(stream-&gt;Read(&amp;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">&quot;1&quot;</span>);</div><div class="line">    EXPECT_TRUE(stream-&gt;Write(request));</div><div class="line">    EXPECT_TRUE(stream-&gt;Read(&amp;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">&quot;2&quot;</span>);</div><div class="line">    EXPECT_TRUE(stream-&gt;Write(request));</div><div class="line">    EXPECT_TRUE(stream-&gt;Read(&amp;response));</div><div class="line">    EXPECT_EQ(response.message(), request.message());</div><div class="line"></div><div class="line">    stream-&gt;WritesDone();</div><div class="line">    EXPECT_FALSE(stream-&gt;Read(&amp;response));</div><div class="line"></div><div class="line">    Status s = stream-&gt;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>
<p>Unary RPC:</p>
<div class="fragment"><div class="line">MockEchoTestServiceStub stub;</div><div class="line">EchoResponse resp;</div><div class="line">resp.set_message(<span class="stringliteral">&quot;hello world&quot;</span>);</div><div class="line">Expect_CALL(stub, Echo(_,_,_)).Times(Atleast(1)).WillOnce(DoAll(SetArgPointee&lt;2&gt;(resp), Return(Status::OK)));</div><div class="line">FakeClient client(stub);</div><div class="line">client.DoEcho();</div></div><!-- fragment --><p>Streaming RPC:</p>
<div class="fragment"><div class="line">ACTION_P(copy, msg) {</div><div class="line">  arg0-&gt;set_message(msg-&gt;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&lt;EchoRequest, EchoResponse&gt;();</div><div class="line">EchoRequest msg;</div><div class="line">EXPECT_CALL(*rw, Write(_, _)).Times(3).WillRepeatedly(DoAll(SaveArg&lt;0&gt;(&amp;msg), Return(<span class="keyword">true</span>)));</div><div class="line">EXPECT_CALL(*rw, Read(_)).</div><div class="line">      WillOnce(DoAll(WithArg&lt;0&gt;(copy(&amp;msg)), Return(<span class="keyword">true</span>))).</div><div class="line">      WillOnce(DoAll(WithArg&lt;0&gt;(copy(&amp;msg)), Return(<span class="keyword">true</span>))).</div><div class="line">      WillOnce(DoAll(WithArg&lt;0&gt;(copy(&amp;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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