https://github.com/googleapis/google-cloud-go/issues/1938

main.go

package main

import (
	"context"

	"cloud.google.com/go/pubsub"
	"cloud.google.com/go/pubsub/pstest"
	"google.golang.org/api/option"
	"google.golang.org/grpc"
)

func main() {
	srv := pstest.NewServer()
	conn, _ := grpc.Dial(srv.Addr, grpc.WithInsecure())
	defer srv.Close()
	defer conn.Close()

	c, _ := pubsub.NewClient(context.Background(), "project", option.WithGRPCConn(conn))

	ctx := context.Background()

	topic, _ := c.CreateTopic(ctx, "topic")
	sub, _ := c.CreateSubscription(ctx, "sub", pubsub.SubscriptionConfig{Topic: topic})
	topic.Delete(ctx)
	sub.Delete(ctx)
}

output

panic: close of closed channel

goroutine 52 [running]:
cloud.google.com/go/pubsub/pstest.(*subscription).stop(...)
	cloud.google.com/go/pubsub/pstest/fake.go:591
cloud.google.com/go/pubsub/pstest.(*GServer).DeleteSubscription(0xc0000be138, 0x16ef8e0, 0xc0004011a0, 0xc0004011d0, 0x0, 0x0, 0x0)
	cloud.google.com/go/pubsub/pstest/fake.go:470 +0xfd
google.golang.org/genproto/googleapis/pubsub/v1._Subscriber_DeleteSubscription_Handler(0x16086a0, 0xc0000be138, 0x16ef8e0, 0xc0004011a0, 0xc000486a80, 0x0, 0x16ef8e0, 0xc0004011a0, 0xc0004c4330, 0x24)
	google.golang.org/genproto/googleapis/pubsub/v1/pubsub.pb.go:3645 +0x217
google.golang.org/grpc.(*Server).processUnaryRPC(0xc0000d0f20, 0x16f48c0, 0xc0003a2480, 0xc0004c8600, 0xc000122d20, 0x1afec40, 0x0, 0x0, 0x0)
	google.golang.org/grpc/server.go:995 +0x460
google.golang.org/grpc.(*Server).handleStream(0xc0000d0f20, 0x16f48c0, 0xc0003a2480, 0xc0004c8600, 0x0)
	google.golang.org/grpc/server.go:1275 +0xd3d
google.golang.org/grpc.(*Server).serveStreams.func1.1(0xc00039c060, 0xc0000d0f20, 0x16f48c0, 0xc0003a2480, 0xc0004c8600)
	google.golang.org/grpc/server.go:710 +0xa1
created by google.golang.org/grpc.(*Server).serveStreams.func1
	google.golang.org/grpc/server.go:708 +0xa1