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# How to write unit tests for gRPC C client.
tl;dr: [Example code](https://github.com/grpc/grpc/blob/master/test/cpp/end2end/mock_test.cc).
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.
For instance, consider an EchoService like this:
```proto
service EchoTestService {
rpc Echo(EchoRequest) returns (EchoResponse);
rpc BidiStream(stream EchoRequest) returns (stream EchoResponse);
}
```
The code generated would look something like this:
```c
class EchoTestService final {
public:
class StubInterface {
virtual ::grpc::Status Echo(::grpc::ClientContext* context, const ::grpc::testing::EchoRequest& request, ::grpc::testing::EchoResponse* response) = 0;
…
std::unique_ptr< ::grpc::ClientReaderWriterInterface< ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse>> BidiStream(::grpc::ClientContext* context) {
return std::unique_ptr< ::grpc::ClientReaderWriterInterface< ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse>>(BidiStreamRaw(context));
}
…
private:
virtual ::grpc::ClientReaderWriterInterface< ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse>* BidiStreamRaw(::grpc::ClientContext* context) = 0;
…
} // End StubInterface
…
} // End EchoTestService
```
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.
A mock for this StubInterface will look like this:
```c
class MockEchoTestServiceStub : public EchoTestService::StubInterface {
public:
MOCK_METHOD3(Echo, ::grpc::Status(::grpc::ClientContext* context, const ::grpc::testing::EchoRequest& request, ::grpc::testing::EchoResponse* response));
MOCK_METHOD1(BidiStreamRaw, ::grpc::ClientReaderWriterInterface< ::grpc::testing::EchoRequest, ::grpc::testing::EchoResponse>*(::grpc::ClientContext* context));
};
```
**Generating mock code:**
Such a mock can be auto-generated by:
1. Setting flag(generate_mock_code=true) on grpc plugin for protoc, or
1. Setting an attribute(generate_mock) in your bazel rule.
Protoc plugin flag:
```sh
protoc -I . --grpc_out=generate_mock_code=true:. --plugin=protoc-gen-grpc=`which grpc_cpp_plugin` echo.proto
```
Bazel rule:
```py
grpc_proto_library(
name = "echo_proto",
srcs = ["echo.proto"],
generate_mock = True,
)
```
By adding such a flag now a header file `echo_mock.grpc.pb.h` containing the mocked stub will also be generated.
This header file can then be included in test files along with a gmock dependency.
**Writing tests with mocked Stub.**
Consider the following client a user might have:
```c
class FakeClient {
public:
explicit FakeClient(EchoTestService::StubInterface* stub) : stub_(stub) {}
void DoEcho() {
ClientContext context;
EchoRequest request;
EchoResponse response;
request.set_message("hello world");
Status s = stub_->Echo(&context, request, &response);
EXPECT_EQ(request.message(), response.message());
EXPECT_TRUE(s.ok());
}
void DoBidiStream() {
EchoRequest request;
EchoResponse response;
ClientContext context;
grpc::string msg("hello");
std::unique_ptr<ClientReaderWriterInterface<EchoRequest, EchoResponse>>
stream = stub_->BidiStream(&context);
request.set_message(msg "0");
EXPECT_TRUE(stream->Write(request));
EXPECT_TRUE(stream->Read(&response));
EXPECT_EQ(response.message(), request.message());
request.set_message(msg "1");
EXPECT_TRUE(stream->Write(request));
EXPECT_TRUE(stream->Read(&response));
EXPECT_EQ(response.message(), request.message());
request.set_message(msg "2");
EXPECT_TRUE(stream->Write(request));
EXPECT_TRUE(stream->Read(&response));
EXPECT_EQ(response.message(), request.message());
stream->WritesDone();
EXPECT_FALSE(stream->Read(&response));
Status s = stream->Finish();
EXPECT_TRUE(s.ok());
}
void ResetStub(EchoTestService::StubInterface* stub) { stub_ = stub; }
private:
EchoTestService::StubInterface* stub_;
};
```
A test could initialize this FakeClient with a mocked stub having set expectations on it:
Unary RPC:
```c
MockEchoTestServiceStub stub;
EchoResponse resp;
resp.set_message("hello world");
Expect_CALL(stub, Echo(_,_,_)).Times(Atleast(1)).WillOnce(DoAll(SetArgPointee<2>(resp), Return(Status::OK)));
FakeClient client(stub);
client.DoEcho();
```
Streaming RPC:
```c
ACTION_P(copy, msg) {
arg0->set_message(msg->message());
}
auto rw = new MockClientReaderWriter<EchoRequest, EchoResponse>();
EchoRequest msg;
EXPECT_CALL(*rw, Write(_, _)).Times(3).WillRepeatedly(DoAll(SaveArg<0>(&msg), Return(true)));
EXPECT_CALL(*rw, Read(_)).
WillOnce(DoAll(WithArg<0>(copy(&msg)), Return(true))).
WillOnce(DoAll(WithArg<0>(copy(&msg)), Return(true))).
WillOnce(DoAll(WithArg<0>(copy(&msg)), Return(true))).
WillOnce(Return(false));
MockEchoTestServiceStub stub;
EXPECT_CALL(stub, BidiStreamRaw(_)).Times(AtLeast(1)).WillOnce(Return(rw));
FakeClient client(stub);
client.DoBidiStream();
```
|
