GCR

# in some test initializer
GCR.cassette_dir = Rails.root.join("test/fixtures/my_grpc_service")
GCR.stub = MyGRPCServer.stub

# in your test code
test "MyController#index works" do
  GCR.with_cassette("some cassette name") do
    MyGRPCServer.do_something
  end
end