Async test method must have non-generic Task return type when no result is expected

[mikkelbu]

We should warn about the following problem

Message: Async test method must have non-generic Task return type when no result is expected

    [Test]
    public async Task<int> AsyncGenericTask()
    {
      return await Task.FromResult(1);
    }

and

    [Test]
    public Task<int> NonAsyncGenericTask()
    {
      return Task.FromResult(1);
    }

and
**