added an extra message check to the client test

client_test.go

@@ -43,4 +43,13 @@ func TestClient(t *testing.T) {
 	if got := doc.Contents(); got != "alphabet" {
 		t.Errorf("saw doc %q, expected %q", got, "alphabet")
 	}
+
+	select {
+	case <-bobCh:
+		t.Error("got an unexpected message via Bob")
+	case <-aliceCh:
+		t.Error("got an unexpected message via Alice")
+	case <-time.After(100 * time.Millisecond):
+		// expected
+	}
 }