Collaboration Julien/Tobias topic

[julien-boudry]

@toddy15

(also #67)

[toddy15]

Alright, I've just created a new PR for infection. You might need to mark it as "Draft". There are a few commits after a first (minimal) run of infection, please take a look.

I've just run infection on the file "Candidate.php" and it already spotted 4 escaped mutants. All of those are now fixed -- either in the code or in the tests.