StrictRetryHelper.cs

internal static class RetryHelper
{
    public static async Task ExecuteAsync(Func<Task> test, int maxAttempts = 5, Func<int, int> backoffFunc = null);
}

// Throws custom exceptions, which trigger retries:
internal static class TryAssert 
{
    public static void Equal(...);
    public static void True(...);
    public static void False(...);
}

public class TestClass
{
    [Fact]
    public async SomeTest()
    {
        await RetryHelper.ExecuteAsync(() => {

            // To make sure we don't do unintentional retries, failing standard Xunit asserts shall trigger test failures:
            Assert.True(...);

            // We need to pick the cases when we want to retry explicitly:
            TryAssert.True(...);

        }, 10);
    }   
}