Unit tests in `FiniteSetsExtTests` rely on specific line numbers

[will62794]

These unit tests in FiniteSetsExtTests rely on specific line numbers of statements in the FiniteSetsExt.tla module. So, if one tries to modify FiniteSetsExt.tla in a way that shifts existing statements to different line numbers, it breaks these tests. These tests should be updated to avoid dependence on specific line numbers.

[lemmy]

This is not limited to FiniteSetsExtTests but how most tests are written. The second paragraph in https://github.com/tlaplus/CommunityModules#contributing also warns about this. A workaround is to only append tests to an existing test module. I suggest this be added to https://github.com/tlaplus/CommunityModules#contributing.