Hi, thanks for posting! Undo operations are considered the same as any other change to a source file, so it's far more likely that the change you made landed in an area that the impact detection didn't properly detect. Right now impact detection will only work for tests that actually have coverage in the same file you are changing, so it can be a bit limited. One way to tell whether it's the change detection or the impact detection is to check for a build - if the build ran but your tests didn't, then it's the impact detection (and you should consider using a different engine mode).