Mock real gRPC server responses - integration-testing

Question

We have a microservice that needs to be integration tested (real calls, but no network communication with anything outside of the test namespace in kubernetes) in our pipeline. It also relies on an external gRPC server which we have no control over.
Above is a picture of what we'd like to have happen. The white box on the left is code that provides the Microservice Boundary with 'external' data. It then keeps calling the Code via REST until it gets back the proper number of records or it times out. The Code pulls records from an internal database, as well as data associated to those records from a gRPC call. Since we do not own the gRPC service, but are doing integration tests, we need a few pre-defined responses to the two gRPC services we call (blue box).
Since our integration tests are self-contained right now, and we don't want to write an entirely new actual gRPC server implementation just to mimick calls, is there a way to stand up a real gRPC server and configure it to return responses? The request is pretty much like a mock setup, except with an actual server.
We need to be able to:
give the server multiple proto files to interpret and have it expose those as endpoints. Proto files must be able to have different package names
using files we can store in source control, configure the responses to each call
able to run in a linux docker container (no windows)
I did find gripmock which seemed almost exactly what we need, but it only serves one proto file per container. It supposedly can serve more than one, but I can't get it to work and their example that serves two files implies each proto file must have the same package name which will likely never happen with our scenarios. In the meantime we are using it, but if we have 10 gRPC call dependencies, we now have to run 10 gripmock servers.

Answer 1

Wikipedia contains a list of API mocking tools. Looking at that list today there is a commercial tool that supports gRPC called Traffic Parrot which allows you to create gRPC mocks based on your Proto files. You can give it multiple proto files, store the mocks in Git and run the tool in Docker.
There are also open-source tools like GripMock but it does not generate stubs based on Proto files, you have to create them manually. Also, the project up to today was not keeping up to date with Proto and gRPC developments i.e. the package name issue you have discovered yourself above (works only if the package names in different proto files are the same). There are a few other open-source tools like grpc-wiremock, grpc-mock or bloomrpc-mock but they still lack widespread adoption and hence might be risky to adopt for an important enterprise project.
Keep in mind, the mock generated will be only a test double, it will not replicate the full behaviour of the system the Proto file corresponds to. If you wanted to also replicate partially the semantics of the messages consider doing a recording of the gRPC messages to create the mocks, that way you can see the sample data as well.

Answer 2

Take a look at this JS library which hopefully does what you need:
https://github.com/alenon/grpc-mock-server
Usage example:
private static readonly PROTO_PATH: string = __dirname + "example.proto";
private static readonly PKG_NAME: string = "com.alenon.example";
private static readonly SERVICE_NAME: string = "ExampleService";
...
const implementations = {
ex1: (call: any, callback: any) => {
const response: any =
new this.proto.ExampleResponse.constructor({msg: "the response message"});
callback(null, response);
},
};
this.server.addService(PROTO_PATH, PKG_NAME, SERVICE_NAME, implementations);
this.server.start();