Use golang to setUp & tearDown for tests

Right now the makefile approach does not even work on MacOS, because it seems like `trap '$(MAKE) mocks-teardown' EXIT` is ignored and runs immediately (thus tearing down mocks _before_ the tests run).

Also, for windows, it seems like a mess to support it, considering that it's not trivial on MacOS (which is also a *NIX)

Using golang for this:

- Makes the Makefile cleaner
- Improves the 'making tests run on all platforms' situation