== Why is this an issue?

Using `Thread.Sleep` in a test might introduce unpredictable and incosistent 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,csharp,diff-id=1,diff-type=noncompliant]
----
[TestMethod]
public void SomeTest()
{
    Thread.Sleep(500); // Noncompliant
    // assertions...
}
----

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 **cancelled and continued**, which gives more flexibility and control in the timing of your code

[source,csharp,diff-id=1,diff-type=compliant]
----
[TestMethod]
public async Task SomeTest()
{
    await Task.Delay(500);
    // assertions...
}
----

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,csharp,diff-id=2,diff-type=noncompliant]
----
[TestMethod]
public void UserService_Test()
{
    var userService = new Mock<UserService>();
    var expected = new User();

    userService
        .Setup(m => m.GetUserById(42))
        .Returns(() =>
        {
            Thread.Sleep(500); // Noncompliant
            return Task.FromResult(expected);
        });

    // assertions...
}
----

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

[source,csharp,diff-id=2,diff-type=compliant]
----
[TestMethod]
public void UserService_Test()
{
    var userService = new Mock<UserService>();
    var expected = new User();

    userService
        .Setup(m => m.GetUserById(42))
        .ReturnsAsync(expected, TimeSpan.FromMilliseconds(500)); 

    // assertions...
}
----

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