Testing a gRPC service

If you want to verify that the implementation of the gRPC service does what you expect, then you can just write standard unit tests and ignore networking completely.

For example, make greeter_server_test.go:

func HelloTest(t *testing.T) {
    s := server{}

    // set up test cases
    tests := []struct{
        name string
        want string
    } {
        {
            name: "world",
            want: "Hello world",
        },
        {
            name: "123",
            want: "Hello 123",
        },
    }

    for _, tt := range tests {
        req := &pb.HelloRequest{Name: tt.name}
        resp, err := s.SayHello(context.Background(), req)
        if err != nil {
            t.Errorf("HelloTest(%v) got unexpected error")
        }
        if resp.Message != tt.want {
            t.Errorf("HelloText(%v)=%v, wanted %v", tt.name, resp.Message, tt.want)
        }
    }
}

I might've messed up the proto syntax a bit doing it from memory, but that's the idea.

I think you're looking for the google.golang.org/grpc/test/bufconn package to help you avoid starting up a service with a real port number, but still allowing testing of streaming RPCs.

import "google.golang.org/grpc/test/bufconn"

const bufSize = 1024 * 1024

var lis *bufconn.Listener

func init() {
    lis = bufconn.Listen(bufSize)
    s := grpc.NewServer()
    pb.RegisterGreeterServer(s, &server{})
    go func() {
        if err := s.Serve(lis); err != nil {
            log.Fatalf("Server exited with error: %v", err)
        }
    }()
}

func bufDialer(context.Context, string) (net.Conn, error) {
    return lis.Dial()
}

func TestSayHello(t *testing.T) {
    ctx := context.Background()
    conn, err := grpc.DialContext(ctx, "bufnet", grpc.WithContextDialer(bufDialer), grpc.WithInsecure())
    if err != nil {
        t.Fatalf("Failed to dial bufnet: %v", err)
    }
    defer conn.Close()
    client := pb.NewGreeterClient(conn)
    resp, err := client.SayHello(ctx, &pb.HelloRequest{"Dr. Seuss"})
    if err != nil {
        t.Fatalf("SayHello failed: %v", err)
    }
    log.Printf("Response: %+v", resp)
    // Test for output here.
}

The benefit of this approach is that you're still getting network behavior, but over an in-memory connection without using OS-level resources like ports that may or may not clean up quickly. And it allows you to test it the way it's actually used, and it gives you proper streaming behavior.

I don't have a streaming example off the top of my head, but the magic sauce is all above. It gives you all of the expected behaviors of a normal network connection. The trick is setting the WithDialer option as shown, using the bufconn package to create a listener that exposes its own dialer. I use this technique all the time for testing gRPC services and it works great.