@rejeep Well, I do not think that order solves this.  As a matter of fact, there cannot be two instances of the same feature within Emacs.   If you force-load `f.el` to test it, all functions for a previously loaded ELPA-installed f.el are re-defined and overwritten.

If you using `ert-runner` to run f.el tests, and ert-runner depends on f.el, you have no choice but use ert-runner with the f.el under test instead of the ELPA f.el.

In fact, I think you need to add the source directory *at the front*, because otherwise your unit tests might accidentally use the ELPA-installed f.el instead of the local one that you actually want to this.

In fact, I recently added assertions similar to [this one in Flycheck](https://github.com/flycheck/flycheck/blob/a1be4e4422f17c3c56ce9c60b1c77f470288df27/test/test-helper.el#L141) to all the `test-helper.el`s in my project to make sure that the tests really run against the source, and not against an ELPA version installed as dependency of a package I use in my tests.