The idea is to find out what can be changed in the code without failing compilation or without failing tests.

For many of those we may expect that it's not explicitly tested but for some it may show that we are not testing something that we believe we are testing.

Tool: https://mutants.rs/getting-started.html, maybe there are others

• try out the tool
• add some tooling to use it easily
• run it on the CI and/or a long-running cloud server.