You recently started working on a new project, or you have been working on it for a while, and it has undergone many changes due to the contributions of multiple developers. This means that you may not be familiar with how the automated tests were written, or how effective they are.

So, how can you be confident that you won't break anything when you deploy new features to production, or when you refactor that old piece of software that's holding you back? Do you have enough trust in your test suite to rely on the fact that a green CI build means that everything is okay?

There are many tools that provide metrics about your code and tests, such as code coverage and CRAP metrics, but they have their limitations.

In this talk, we will explore ways to evaluate the effectiveness of your test suite, how to improve it, and the benefits of having a robust and comprehensive set of automated tests.

I've performed the talk at a couple of technical conferences and meetup, and I will bring it at a testing conference in Canada in September 23 (KWSQA), it's quite a mature and well received talk.
Some of the code snippets are in PHP, but it's language agnostic and I can easily change examples in any other language if needed.