Question

lets say i have a background worker in a class that perform db query in a background thread.

i wanna test this class

so i mock my db and return some collection so far so good,
make sure my background worker called the do work
and than i wanna make sure that the finish also happened.

I’ve noticed that the test pass and fail randomly (i think it has something to do with threads)

any suggestions

Answer 1

You may have a race condition between the background thread and the asserts/verifies.

For example:

[Test]
public void TestWithRaceCondition()
{
    bool called = false;
    new Thread(() => called = true).Start();
    Assert.IsTrue(called);
}

The thread doesn’t necessarily end before the asserts, sometimes it will and sometimes it won’t. A solution to this case is to join the background thread:

[Test]
public void TestWithoutRaceCondition()
{
    bool called = false;
    var thread = new Thread(() => called = true);
    thread.Start();
    thread.Join()
    Assert.IsTrue(called);
}

One way to check if it’s a race condition is to delay the test thread (call Thread.Sleep for long time just before the assert) and if the test stops failing that’s good indication for race condition.