Delay-loading TestCaseSource in NUnit

I have some NUnit tests which uses a TestCaseSource function. Unfortunately, the TestCaseSource function that I need takes a long time to initialize, because it scans a folder tree recursively to find all of the test images that would be passed into the test function. (Alternatively it could load from a file list XML every time it's run, but automatic discovery of new image files is still a requirement.)

Is it possible to specify an NUnit attribute together with TestCaseSource such that NUnit does not enumerate the test cases (does not call the TestCaseSource function) until either the user clicks on the node, or until the test suite is being run?

The need to get all test images stored in a folder is a project requirement because other people who do not have access to the test project will need to add new test images to the folder, without having to modify the test project's source code. They would then be able to view the test resul开发者_StackOverflowt.

Some dogmatic unit-testers may counter that I am using NUnit to do something it's not supposed to do. I have to admit that I have to meet a requirement, and NUnit is such a great tool with a great GUI that satisfies most of my requirements, such that I do not care about whether it is proper unit testing or not.

Additional info (from NUnit documentation)

Note on Object Construction

NUnit locates the test cases at the time the tests are loaded, creates instances of each class with non-static sources and builds a list of tests to be executed. Each source object is only created once at this time and is destroyed after all tests are loaded.

If the data source is in the test fixture itself, the object is created using the appropriate constructor for the fixture parameters provided on the TestFixtureAttribute or the default constructor if no parameters were specified. Since this object is destroyed before the tests are run, no communication is possible between these two phases - or between different runs - except through the parameters themselves.

It seems the purpose of loading the test cases up front is to avoid having communications (or side-effects) between TestCaseSource and the execution of the tests. Is this true? Is this the only reason to require test cases to be loaded up front?

Note:

A modification of NUnit was needed, as documented in http://blog.sponholtz.com/2012/02/late-binded-parameterized-tests-in.html

There are plans to introduce this option to later versions of NUnit.

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I don't know of a way to delay-load test names in the GUI. My recommendation would be to move those tests to a separate assembly. That way, you can quickly run all of your other tests, and load the slower exhaustive tests only when needed.