How to Write a Regression Test for a Fixed Bug

A bug that keeps returning has no regression test. Writing one locks the fix in. Here is how.

How to fix it

1. Reproduce the bug in a test

Capture the exact conditions that triggered the bug in an automated test, and assert the correct behavior. The test should fail against the unfixed code, proving it captures the bug.

2. Add it to the suite

Put the test in the suite that runs on every change, so if a future edit reintroduces the bug, the test fails immediately. This is what stops the bug from quietly coming back.

3. Confirm fail-then-pass

Verify the test fails before the fix and passes after. A regression test that passes even without the fix does not actually guard against the bug — it must demonstrably catch it.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.