Deadlock when mocking RPCs that get called in a non-deterministic order

[seanlafferty-ibm]

I have a couple of different client streams within the same service that get written to via select statements in for loops, so which stream gets written to first is non-deterministic. What I care to test is that when I advance the clock in testing/synctest that both ended up having received a message.

I was thinking I could achieve this with the FirstMatch() planner

mockServer.ExpectClientStream(myMethod1).Times(1).Return(resp1)
mockServer.ExpectClientStream(myMethod2).Times(1).Return(resp2)
// do stuff
synctest.Wait()
// test ends, let grpcmock error if both were not called exactly once

but I'm observing that grpcmock can deadlock if the order of expectations does not match the order that the app calls the rpcs.

Here's a reproduction

import (
	"fmt"
	"testing"

	"go.nhat.io/grpcmock"
	"go.nhat.io/grpcmock/planner"
	testpb "go.nhat.io/grpcmock/test/grpctest"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"
	"gotest.tools/v3/assert"
)

func TestBlocking(t *testing.T) {
	mockServer, mockDialer := grpcmock.MockServerWithBufConn(
		grpcmock.WithPlanner(planner.FirstMatch()),
		grpcmock.RegisterService(testpb.RegisterItemServiceServer),
	)(t)
	conn, err := grpc.NewClient("passthrough:mockURL", grpc.WithContextDialer(mockDialer), grpc.WithTransportCredentials(insecure.NewCredentials()))
	t.Cleanup(func() {
		err := conn.Close()
		if err != nil {
			t.Fatal(err)
		}
	})
	assert.NilError(t, err)
	client := testpb.NewItemServiceClient(conn)
	stream1, err := client.CreateItems(t.Context())
	assert.NilError(t, err)

	mockServer.ExpectUnary(testpb.ItemService_GetItem_FullMethodName).Times(1).Return(testpb.Item{})
	mockServer.ExpectClientStream(testpb.ItemService_CreateItems_FullMethodName).Times(1).Return(&testpb.CreateItemsResponse{})
	err = stream1.Send(&testpb.Item{Id: 52})
	fmt.Println("this prints")
	_, err = client.GetItem(t.Context(), &testpb.GetItemRequest{})
	fmt.Println("this does not print")
	assert.NilError(t, err)
}

This blocks, but if you flip the order of the mocks

	mockServer.ExpectClientStream(testpb.ItemService_CreateItems_FullMethodName).Times(1).Return(&testpb.CreateItemsResponse{})
	mockServer.ExpectUnary(testpb.ItemService_GetItem_FullMethodName).Times(1).Return(testpb.Item{})

it stops blocking.