Mocha does not reload modules when running multiple tests.
This can lead to some curious errors that are difficult to understand at first,
but have to do with modules that have an internal state of their own.
If you have a folder with two files, test1.js and test2.js (shown in gist below),
you will find you get different test results even though
they are identical except in name. The first one fails, but the second succeeds.
So some state from previous tests can "pollute" later tests. This makes it difficult to write unit tests
in isolation with Mocha, because suddenly when you put both tests together in the same directoy, mocha's behavior can break