Async unit test in Test Runner

Question

Is it possible to unit test async functions? I can't get it to work.

If I use 'async void', the test always passes, even if the assertion fails. If I use 'async Task', I can't run the test. Unity Test Runner reports: "Method has non-void return value, but no result is expected".

 [Test]
 public async void MyTestFailAsyncVoid()
 {
     await Task.Delay(1000);
     Assert.That(false);
 }
 
 [Test]
 public async Task MyTestFailAsyncTask()
 {
     await Task.Delay(1000);
     Assert.That(false);
 }

Answer 1

In case anybody else cares about this, we found a workaround of sorts.

It uses the 'Async Await Support' library on the Unity Store: link . We added a function to the library to have AsIEnumerator() return null:

 public static IEnumerator AsIEnumeratorReturnNull<T>(this Task<T> task)
 {
     while (!task.IsCompleted)
     {
         yield return null;
     }
 
     if (task.IsFaulted)
     {
         ExceptionDispatchInfo.Capture(task.Exception).Throw();
     }
 
     yield return null;
 }

An async test looks like this:

 [UnityTest]
 public IEnumerator MyAsyncTest()
 {
     var task = MyObject.SomeAsyncCall();
     yield return task.AsIEnumeratorReturnNull();
 
     var returnValue = task.Result;
     Assert.AreEqual(expectedReturnValue, returnValue);
 }

An async test that should throw an exception looks like this:

 [UnityTest]
 public IEnumerator MyAsyncTestThatShouldThrow()
 {
     async Task<bool> FailsWithException()
     {
         try
         {
             await MyObject.SomeAsyncCall();
         }
         catch (Exception)
         {
             return true;
         }
 
         return false;
     }
 
     var task = FailsWithException();
     yield return task.AsIEnumerator();
     
     var threwException = task.Result;
 
     Assert.That(threwException);
 }

Answer 2

Based on this thread https://forum.unity.com/threads/async-await-in-unittests.513857/#post-6046400 You can use the following helpers

     public static class UnityTestUtils {
  
         public static T RunAsyncMethodSync<T>(Func<Task<T>> asyncFunc) {
             return Task.Run(async () => await asyncFunc()).GetAwaiter().GetResult();
         }
         public static void RunAsyncMethodSync(Func<Task> asyncFunc) {
             Task.Run(async () => await asyncFunc()).GetAwaiter().GetResult();
         }
 }

Usage:

     [Test]
     public void Test()
     {
         var result = RunAsyncMethodSync(() => GetTestTaskAsync(4));
         Assert.That(result, Is.EqualTo(4));
     }
 
     public async Task<int> GetTestTaskAsync(int a) {
         await Task.Delay(TimeSpan.FromMilliseconds(200));
         return a;
     }
 
     [Test]
     public void Testthrow() {
         Assert.Throws<InvalidOperationException>(
                        ()=> RunAsyncMethodSync(() => ThrowTaskAsync(4)));
     }
 
     public async Task<int> ThrowTaskAsync(int a) {
         await Task.Delay(TimeSpan.FromMilliseconds(200));
         throw new InvalidOperationException();
     }

Answer 3

Answer by ochir_d · May 25, 2021 at 12:37 AM

Utils

    public static class UnityTestUtils {
      public static void RunAsyncMethodSync(this Func < Task > asyncFunc) {
        Task.Run(async () => await asyncFunc()).GetAwaiter().GetResult();
      }
    }

Usage

 public class AsyncAwaitUnitTests {
      [Test]
      public void WithExt([Values(0, 500, 1000)] int delay) {
        UnityTestUtils.RunAsyncMethodSync(async () => {
          var sw = Stopwatch.StartNew();
 
          await Task.Delay(delay);
 
          Assert.AreEqual(delay, (int) sw.Elapsed.TotalMilliseconds, 300);
        });
      }
    }

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