I have this process which can be started and stopped. When started it will periodically perform some task, for which it will need to use an instance of another type that is created using some input, so it takes factory method as constructor input and it should invoke the factory each time it performs the task. In the test setting "periodically" …

gistfile1.cs

public void Start_InvokesFactoryMethod()
{
    // Arrange
    
    // set up mocks and stuff needed (removed for brevity)
    
    bool testTimedOut;
    using (AutoResetEvent waitHandle = new AutoResetEvent(false))
    {
        Func<ISomeResource, IMyObject> myObjectProvider = resource =>
            {
                waitHandle.Set();
                return new Mock<IMyObject>();
            };

        TypeThatIsTested instance = new TypeThatIsTested(myObjectProvider);

        // Act
        instance.Start();

        testTimedOut = !waitHandle.WaitOne(TimeSpan.FromSeconds(2));
    }

    // Assert
    Assert.IsFalse(testTimedOut, "Test timed out");
}