MessagingCenter callback fails to register

Issue

I'm making an app with xamarin.forms and I have an issue with unit testing part. The problem is that when the test case runs isolated it passes, but when I run all the tests it fails.

using EmpresaPersonal.Modelos;
using EmpresaPersonal.ModelosVisuales;
using EmpresaPersonal.Services;
using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xunit;

namespace EmpresaPersonal.Test
{
    public class PruebasVMEditarContacto
    {
        [Fact]
        public async Task GuardarContactoSeteaCorrectamenteAsync()
        {
            // Preparamos el editor y los eventos
            var store = new MockDataStore();
            var mockNavegacion = ServiciosFalsos.MockIrAtras();
            var editor = new MVEditarContacto(store, mockNavegacion.Object)
            {
            // Initializer setters...
            };

            bool llamado = false;
            MessagingCenter.Subscribe<MVEditarContacto, string>(this, MVEditarContacto.EventoContactoCreado, async (s, idContacto) => // This line throws a NullReferenceException
            {
                var contacto = await store.GetItemAsync(idContacto);
                // Algunos chequeos van por acá
                Assert.NotNull(contacto);
                Assert.Equal(editor.Nombre.Valor, contacto.Nombre);
                Assert.Equal(editor.Empresa.Valor, contacto.Empresa);
                Assert.Equal(editor.TelefonoPrincipal.Valor, contacto.TelefonoPrincipal);
                Assert.Equal(editor.TelefonoSecundario.Valor, contacto.TelefonoSecundario);
                llamado = true;
            });
            editor.GuardarContacto.Execute(null);
            await editor.EsperarCompletarAsync();
            Assert.True(llamado, "El evento no fue llamado.");
            mockNavegacion.Verify(m => m.AtrasAsync());
        }
    }
}

I don't use anything than MessagingCenter.Send` from the model instantiated in this chunk. I have to say that I have another test for a model that subscribes to this model, to the same event in it's constructor (the model is the subscriber).

Any ideas?

Solution

I saw that when unit testing very xamarin.forms related code such MessagingCenter, the best way is to run the tests from Xunit.Runner.Devices test runner (A.C.A. with a real and initialized xamarin.forms environment).

The best example I've found is the EShop on containers mobile app.

I've just left my project and started a new one heavily based on Prism.Forms to ease unit testing these kind of things because it is constructed on top of IOC containers.

Answered By - Fran