Occasionally, the requirement for merge request or pull request to be “green” is to have test coverage % that greater or at least equal to the test coverage % of the previous run.

This requirement is counter-productive, because a drop in test coverage % does not imply that the test coverage is worse. For example, in a codebase with 90% test coverage, deleting a chunk of dead code that has 100% coverage will make the test coverage drop to below 90%.