Great question, Thomas. Thanks for asking.
My go to “good” test: Did my session yield information that started a useful conversation and did this lead to a decision that helped my team move forward in the right direction?”. I feel I’m adding value if the answer is mostly yes.
I think it’s awesome you called out self-reflection. Such an important part of improving our skill as exploratory tester. Sometimes “doing better” is as simple as running another charter/session. And this is why I prefer short time boxed sessions, say 30 to 45 minutes. My feedback loop is short if I know I could’ve done better.
I once worked in a team where at the end of a time-boxed testing session I’d debrief my testing notes in person with another tester – preferably as close to as soon as I’d finished my session. I found this an incredibly useful way to get instant feedback on my approach and discoveries. Particularly useful when I first joined the team.
I’d love to find a simple way to track exploratory testing effectiveness over the course of a project. And maybe that’s as simple as counting the velocity of testing sessions. Diving into testing metrics is an interesting topic that perhaps warrants a whole power hour!
Though I’ve never done this before, perhaps there’s an opportunity to use a Net Promoter Score (NPS) approach. For example, take a useful sample set of colleagues and ask: “On a scale of 1 to 10, how likely are you to recommend my exploratory testing skills/services?” (Where 10 is a slam dunk “Always” and 1 is a “No chance!”. And run this periodically to track trends.