xUnit1030 Warning

Do not call ConfigureAwait in test method

Cause

Developers should not call ConfigureAwait(false) against tasks in a test method, as this may cause parallelization issues like running too many tests in parallel.

Reason for rule

Calling ConfigureAwait (with false, specifically) will cause any code after the awaited task to run on a thread pool thread, which can grow without limit. xUnit.net uses its own special thread pool to limit the number of tests which can actively run in parallel.

This only affects test methods marked with [Fact] or [Theory]. It does not apply to any third party test methods or test any non-test methods.

CA2007 forces users to write ConfigureAwait regardless of the situation, so if you’ve enabled this rule, you may write .ConfigureAwait(true) and this rule will not trigger. However, this comes with at least two side effects. First, the call is not free; it always allocates at least one (or more) unnecessary objects, even when the net result should be the same, in addition to spending the time to execute all the involve code. Second, the call is not always transparent; when used in the context of await using of a newly constructed object, the result type from ConfigureAwait overwrites the type of your object, so you will be unable to use the newly constructed object in any way due to the incompatible type that is returned. It is for reasons like these that we strongly recommend you disable CA2007 in your unit test projects, especially when feeling any of the friction involved with this.

How to fix violations

To fix a violation of this rule, remove the call to ConfigureAwait or use a true value.

Examples

Violates

using System.Threading.Tasks;
using Xunit;

public class xUnit1030
{
    [Fact]
    public async Task TestMethod()
    {
        await Task.Delay(1).ConfigureAwait(false);

        // ...code running on thread pool thread...
    }
}

Does not violate

using System.Threading.Tasks;
using Xunit;

public class xUnit1030
{
    [Fact]
    public async Task TestMethod()
    {
        await Task.Delay(1);

        // ...code running on xUnit.net parallel execution thread pool thread...
    }
}

using System.Threading.Tasks;
using Xunit;

public class xUnit1030
{
    [Fact]
    public async Task TestMethod()
    {
        await Task.Delay(1).ConfigureAwait(true);

        // ...code running on xUnit.net parallel execution thread pool thread...
    }
}