== Why is this an issue?

Using `Thread.Sleep` in a test might introduce unpredictable and inconsistent results depending on the environment. Furthermore, it will block the https://en.wikipedia.org/wiki/Thread_(computing)[thread], which means the system resources are not being fully used.

[source,vbnet,diff-id=1,diff-type=noncompliant]
----
<TestMethod>
Public Sub SomeTest()
    Threading.Thread.Sleep(500) ' Noncompliant
    ' assertions...
End Sub
----

An alternative is a task-based asynchronous approach, using https://learn.microsoft.com/en-us/dotnet/csharp/asynchronous-programming/[async and await].

More specifically the https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.task.delay[Task.Delay] method should be used, because of the following advantages:

* It is **asynchronous**: The thread will not be blocked, but instead will be reused by other operations
* It is more **precise** in timing the delay than `Thread.Sleep`
* It can be **canceled and continued**, which gives more flexibility and control in the timing of your code

[source,vbnet,diff-id=1,diff-type=compliant]
----
<TestMethod>
Public Async Function SomeTest() As Task
    Await Task.Delay(500)
    ' assertions...
End Function
----

Another scenario is when some data might need to be mocked using https://github.com/moq/moq4[Moq], and a delay needs to be introduced:

[source,vbnet,diff-id=2,diff-type=noncompliant]
----
<TestMethod>
Public Sub UserService_Test()
    Dim UserService As New Mock(Of UserService)
    Dim Expected As New User
    UserService.Setup(Function(X) X.GetUserById(42)).Returns(
        Function()
            Threading.Thread.Sleep(500) ' Noncompliant
            Return Task.FromResult(Expected)
        End Function)
    ' assertions...
End Sub
----

An alternative to `Thread.Sleep` while mocking with `Moq` is to use `ReturnsAsync` and pass the amount of time to delay there:

[source,vbnet,diff-id=2,diff-type=compliant]
----
<TestMethod>
Public Sub UserService_Test()
    Dim UserService As New Mock(Of UserService)
    Dim Expected As New User
    UserService.Setup(Function(X) X.GetUserById(42)).ReturnsAsync(Expected, TimeSpan.FromMilliseconds(500))
    ' assertions...
End Sub
----

include::../resources-dotnet.adoc[]

include::../rspecator-dotnet.adoc[]