Testing Interceptors in Isolation

[bhollis]

Hi there, we're switching from the Google gRPC libraries to Connect, and so far it's going well. However, we've hit a bit of a snag while trying to migrate over all of our custom interceptors. As far as I can tell, there's no way for us to construct a request.AnyRequest ourselves with a populated spec field, which makes it difficult for us to test an interceptor in isolation. Our interceptor is only reading req.Spec().Procedure and with the Google libraries, it was easy for us to construct a grpc.UnaryServerInfo struct to pass in with all kinds of different method names. With Connect, we can't quite figure out any way to do this. As the docs on AnyRequest say:

// To preserve our ability to add methods to this interface without breaking
// backward compatibility, only types defined in this package can implement
// AnyRequest.

As an example, our original tests looked something like this, where authz.NewInterceptor returned a grpc.UnaryServerInterceptor:

interceptor := authz.NewInterceptor()
info := &grpc.UnaryServerInfo{
  FullMethod: test.method,
}
_, err := interceptor(
  ctx,
  nil,
  info,
  func(_ context.Context, _ any) (any, error) { return nil, nil },
)
assert.ErrorIs(t, err, test.expectedErr)

[jhump]

@bhollis, you can provide your own implementation of AnyRequest, but it must embed a *connect.Request. So you could do something like so:

type testRequest[T any] struct {
	*connect.Request[T]
	method string
}

func (r testRequest[_]) Spec() connect.Spec {
	return connect.Spec{
		Procedure: r.method,
	}
}

func newRequest[T any](msg *T, method string) connect.AnyRequest {
	return testRequest[T]{Request: connect.NewRequest(msg), method: method}
}

Note that such a test request will cause problems if passed to the actual Connect framework, so if your interceptor implementation actually needs to override any of these request properties (and pass the modified request to the next interceptor or handler in the chain), that is not currently possible.

But if you are just testing your interceptor in isolation, this technique should be fine.

[bhollis]

Awesome, thank you.