Xamarin.Forms/Xamarin.Forms.Core.UnitTests/DeviceUnitTests.cs

using System;
using System.Threading.Tasks;
using NUnit.Framework;
using Xamarin.Forms.Internals;

namespace Xamarin.Forms.Core.UnitTests
{
	[TestFixture]
	public class DeviceUnitTests : BaseTestFixture
	{
		[Test]
		public void TestBeginInvokeOnMainThread()
		{
			bool calledFromMainThread = false;
			Device.PlatformServices = MockPlatformServices(() => calledFromMainThread = true);

			bool invoked = false;
			Device.BeginInvokeOnMainThread(() => invoked = true);

			Assert.True(invoked, "Action not invoked.");
			Assert.True(calledFromMainThread, "Action not invoked from main thread.");
		}

		[Test]
		public async Task TestInvokeOnMainThreadWithSyncFunc()
		{
			bool calledFromMainThread = false;
			Device.PlatformServices = MockPlatformServices(() => calledFromMainThread = true);

			bool invoked = false;
			var result = await Device.InvokeOnMainThreadAsync(() => { invoked = true; return true; });

			Assert.True(invoked, "Action not invoked.");
			Assert.True(calledFromMainThread, "Action not invoked from main thread.");
			Assert.True(result, "Unexpected result.");
		}

		[Test]
		public async Task TestInvokeOnMainThreadWithSyncAction()
		{
			bool calledFromMainThread = false;
			Device.PlatformServices = MockPlatformServices(() => calledFromMainThread = true);

			bool invoked = false;
			await Device.InvokeOnMainThreadAsync(() => { invoked = true; });

			Assert.True(invoked, "Action not invoked.");
			Assert.True(calledFromMainThread, "Action not invoked from main thread.");
		}

		[Test]
		public async Task TestInvokeOnMainThreadWithAsyncFunc()
		{
			bool calledFromMainThread = false;
			Device.PlatformServices = MockPlatformServices(() => calledFromMainThread = true,
				invokeOnMainThread: action => Task.Delay(50).ContinueWith(_ => action()));

			bool invoked = false;
			var task = Device.InvokeOnMainThreadAsync(async () => { invoked = true; return true; });
			Assert.True(calledFromMainThread, "Action not invoked from main thread.");
			Assert.False(invoked, "Action invoked early.");

			var result = await task;
			Assert.True(invoked, "Action not invoked.");
			Assert.True(result, "Unexpected result.");
		}

		[Test]
		public async Task TestInvokeOnMainThreadWithAsyncFuncError()
		{
			bool calledFromMainThread = false;
			Device.PlatformServices = MockPlatformServices(() => calledFromMainThread = true,
				invokeOnMainThread: action => Task.Delay(50).ContinueWith(_ => action()));

			bool invoked = false;
			async Task<bool> boom()
			{ invoked = true; throw new ApplicationException(); }
			var task = Device.InvokeOnMainThreadAsync(boom);
			Assert.True(calledFromMainThread, "Action not invoked from main thread.");
			Assert.False(invoked, "Action invoked early.");

			async Task MethodThatThrows() => await task;
			Assert.ThrowsAsync<ApplicationException>(MethodThatThrows);
			Assert.True(invoked, "Action not invoked.");
		}

		[Test]
		public async Task TestInvokeOnMainThreadWithAsyncAction()
		{
			bool calledFromMainThread = false;
			Device.PlatformServices = MockPlatformServices(() => calledFromMainThread = true,
				invokeOnMainThread: action => Task.Delay(50).ContinueWith(_ => action()));

			bool invoked = false;
			var task = Device.InvokeOnMainThreadAsync(async () => { invoked = true; });
			Assert.True(calledFromMainThread, "Action not invoked from main thread.");
			Assert.False(invoked, "Action invoked early.");

			await task;
			Assert.True(invoked, "Action not invoked.");
		}

		[Test]
		public async Task TestInvokeOnMainThreadWithAsyncActionError()
		{
			bool calledFromMainThread = false;
			Device.PlatformServices = MockPlatformServices(() => calledFromMainThread = true,
				invokeOnMainThread: action => Task.Delay(50).ContinueWith(_ => action()));

			bool invoked = false;
			async Task boom()
			{ invoked = true; throw new ApplicationException(); }
			var task = Device.InvokeOnMainThreadAsync(boom);
			Assert.True(calledFromMainThread, "Action not invoked from main thread.");
			Assert.False(invoked, "Action invoked early.");

			async Task MethodThatThrows() => await task;
			Assert.ThrowsAsync<ApplicationException>(MethodThatThrows);
			Assert.True(invoked, "Action not invoked.");
		}

		[Test]
		public void InvokeOnMainThreadThrowsWhenNull()
		{
			Device.PlatformServices = null;
			Assert.Throws<InvalidOperationException>(() => Device.BeginInvokeOnMainThread(() => { }));
			Assert.Throws<InvalidOperationException>(() => Device.InvokeOnMainThreadAsync(() => { }).Wait(100));
			Assert.Throws<InvalidOperationException>(() => Device.InvokeOnMainThreadAsync(() => true).Wait(100));
			Assert.Throws<InvalidOperationException>(() => Device.InvokeOnMainThreadAsync(async () => { }).Wait(100));
			Assert.Throws<InvalidOperationException>(() => Device.InvokeOnMainThreadAsync(async () => true).Wait(100));
		}

		private IPlatformServices MockPlatformServices(Action onInvokeOnMainThread, Action<Action> invokeOnMainThread = null)
		{
			return new MockPlatformServices(
				invokeOnMainThread: action =>
				{
					onInvokeOnMainThread();

					if (invokeOnMainThread == null)
						action();
					else
						invokeOnMainThread(action);
				});
		}
	}
}