This sets up the new `test/unit` and `test/integration` folders
and starts classification of some of the test files.
Note that unit tests include, `fs-utils` and `system-info` tests.
While these tests interact with the filesystem, the implementation
of these modules is simple enough, and the tests are fast enough to
allow these tests to fall under the `unit` test category (according to
test/README)
Change-type: patch
