Metamorphic Testing, a neat technique for transforming test data to generate more inputs to test your software: https://www.hillelwayne.com/post/metamorphic-testing/
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I love how the CommonMark Spec has a test suite that's just a JSON array. It's really easy to test a library for compliance, and I've seen developers nerd-sniped into full compliance.
https://spec.commonmark.org/0.31.2/spec.json
Do any tech streamers try new software live? It'd be a really fun way of doing UX testing.
LLMs seem to handle dependency upgrades really well.
The task is well-specified, there's usually a build/test suite to check correctness of the modifications, and there's often a changelog they can consume too.