One test a day keeps bugs away

This is a quote from a presentation by Diego Aguiar at SymfonyCon that I saw from a tweet from SymfonyCasts.

I haven't seen the rest of the presentation, but I liked this quote and the idea of continuously improving a codebase using automated tests.

The talk was titled "Advanced Test Driven Development" so I assume that it was focused on ensuring that new functionality also has accompanying tests but it could also apply to existing code.

A lot of existing code that I've worked on wasn't covered by tests, so going back and writing tests for that code would be beneficial too - even if it's only one test a day. It would help to prevent and uncover existing bugs, enable the code to be refactored and changed without introducing regressions, and make the codebase more maintainable.

Small changes over time add up.