Fix race

server/server_test.go

@@ -66,6 +66,8 @@ func TestServer_PublishWithFirebase(t *testing.T) {
 	msg1 := toMessage(t, response.Body.String())
 	require.NotEmpty(t, msg1.ID)
 	require.Equal(t, "my first message", msg1.Message)
+
+	time.Sleep(100 * time.Millisecond) // Firebase publishing happens
 	require.Equal(t, 1, len(sender.Messages()))
 	require.Equal(t, "my first message", sender.Messages()[0].Data["message"])
 	require.Equal(t, "my first message", sender.Messages()[0].APNS.Payload.Aps.Alert.Body)