I have to refactor am unit test from NUNIT 2 to NUNIT 3 and the following syntax throws an error:
var expectedResponseMessage = new HttpResponseMessage();
Func<Task<HttpResponseMessage>> continuation =
() => Task.Factory.StartNew(() => expectedResponseMessage);
Error:
Async test method must have non-void return type
How may I rewrite this? I have tried many syntaxes but no luck.
The error
Async test method must have non-void return type
means that in NUnit 3+, an async
Unit Test itself may not have a void
return type (ie the method decorated with [Test] / [TestCase]
etc). Instead, you can return an empty Task
( Correct way in newer versions of NUnit with async test support ):
[Test]
public async Task EnsureFoo()
{
// Arrange
// Act
var myResult = await classBeingTested.DoSomethingAsync();
// Assert
Assert.IsNotNull(myResult);
...
}
In NUnit 2.x, this wasn't checked, so a async void
unit test could slip into your unit test code base, ie of the form ( Bad, don't do this )
[Test]
public async void Foo() // < -- Error : Async test method must have non-void return type
{
var myResult = await classBeingTested.DoSomethingAsync();
// Post continuation assertions here.
}
this is rather dangerous - the test can't be awaited * , and would return before any continuations completed - eg any failures in the Asserts
done in the continuation might not be reported.
Re : Your fake Task
Scheduling a Task just to return a fake response seems overkill, ie in most tests you should be able to use Task.FromResult
to replace:
Func<Task<HttpResponseMessage>> continuation =
() => Task.Factory.StartNew(() => expectedResponseMessage);
With the cheaper:
Func<Task<HttpResponseMessage>> continuation =
() => Task.FromResult(expectedResponseMessage);
Task.FromResult
returns an already completed task with the given return value - in most cases, this should suffice for your unit testing purposes, unless you really do want an independent Task to be executed on the threadpool.
* Actually, seemingly even earlier versions such as NUnit 2.6.4 had already identified the issue with async void
tests, and incorporated a workaround
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