My use case is as follows:

I get external files which I need to parse to extract the data I have to save into a database. I cannot change these external files as that would invalidate the testing of the whole parsing process.

The next step is to save this data into the database, BUT

• The database is live; and
• the testing process might crash and fail to clean-up the data it inserted during testing.

Hence my idea to change the primary keys of the data to be inserted, so

• the other programs using the database recognize the data as test-data and will not use them; and
• it is easy to manually delete the inserted test-data in case the test script crashed and failed to clean-up.

For that to work I had thought it would be easiest if my module would "know" when it was being tested, so it could manipulate the test data as explained above. Rather than relying on environment variables, external semaphore files or additional attributes on the module's object (all of which a programmer might forget to set or provide), I was looking for a solution which could be built-in, but it seems there is no easy fool-proof automatic way to check if a module is being "tested".