Lazy loading of assemblies can be tricky

NUnit error message on data-driven test: `Test` is Inconclusive

ReSharper Test Runner warning: Element `Test` was left pending after its run completion.

Recently I was doing some testing and trying to check if all classes have a corresponding test class. Therefore I used data-driven NUnit tests, which uses a list of all classes in non-test assemblies.

I created another test to verify the list of the classes used as test data-source. The idea was to make sure that the data source is returning all testable classes

and excludes classes that are not in the scope for the „test class required“ constraint.

The classes are added correctly to the data-driven data source but the tests were not executed. The test runner marked the test as “ignored” and “inconclusive”. So I was trying to figure out, why were the tests (for approx. 100 classes) not executed, although I validated, that the data source is correct.

After using multiple test runners and searching the internet for bugs, the solution came to my mind. **The .NET framework only loads an assembly to the app domain if it is required.** The data-source validation test was using at least one class from each related assembly. The framework loads the assembly to the app domain before the test method was executed.

For the data-driven test, it was different. None of these classes was referenced, so the .NET framework does not load the assemblies into the app domain. The solution is to make the data-source reference the types from the related assemblies. After that, it was working fine and all classes were tested.