On 2017-04-26 the Symfony User Group Cologne gave me the opportunity to speak about Code Coverage.

If you create software that is planned for continuous enhancements and maintenance over several years then you’ll need a sustainable strategy for code quality.
Code coverage by automated tests is one important metric, and its value should equal 100% at all times.
My talk shows why this is so and how it can be achieved in PHP / Symfony based applications.

See the full presentation at Speaker Deck