NUnit Test Debugging

Question

I'm working on a Geometry library. There are 200+ unit tests.

There's a particularly stubborn test that fails whenever I select "Run All", but the test passes when I run that test individually, or use the debugger on it. I do believe the issue showed up about when I shifted over from visual studio '13 to the '15 edition.

Now some notes about the geometry library:

The objects are immutable.

The tests have no shared objects between them.

So my Question: What are the possible causes for this odd behavior?

Edit:

[Test()]
public void Plane_IntersectionWithPlane_IdenticalPlane()
{
     Plane testPlane = new Plane(new Direction(Point.MakePointWithInches(2, -1, 1)), 
                                               Point.MakePointWithInches(2, 1, 2));
     Line found = (testPlane.Intersection(testPlane));

     Line expected = new Line(new Direction(Point.MakePointWithInches(0, -1, -1)), 
                                            Point.MakePointWithInches(2, 1, 2));
     Assert.IsTrue(found.Equals(expected));
}

Answer 1

I've come across similar issues in the past, but it's always turned out to be some unexpected interaction between the underlying code elements, or the way that the tests have been written. Some issues to check are:

• Static object construction / destruction
• Synchronisation issues
• Mock setup / cleanup issues

I've found the best approach to track down the issue is follow an approach similar to that suggested by @Matthew Strawbridge in the comments. I add Ignore attributes to Tests/TestFixtures to remove tests until the run-all starts working and then start adding them back in until it breaks again narrowing down the problem.

Sometimes you will also find that ignoring the test that is currently failing will cause another test to fail instead. This is a good indication that the problem is actually being caused by another one of your tests not cleaning up after itself correctly.

Looking at the code between the tests that fail/seem to cause the fail can then help you to narrow down the interaction. The error/failure reason for the tests can also help of course...

Selecting 'Run-all' runs all of the tests in a predictable order, so the tests will generally be run the same way everytime. If you select a batch of tests then it's possible that the runner may choose to run them in a different order, based around your selection order which may be why you've experience different behaviour when selecting tests, rather than using run-all.

Answer 2

Try the following:

Open Nunit GUI And before you run the test change the above in the settings:

It helped me once detect my problems.

BTW: what version of NUNIT are you using ? If you don't know what is Nunit GUI then you probably didn't downloaded Nunit separately. You can get the install from here :

http://www.nunit.org/index.php?p=download