What causes a singleton holding state across tests?

The singleton's static instance and its fields persist for the whole process, so a test that mutates the singleton leaves dirty state that the next test inherits.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix a Singleton Holding State Across Tests

Quick answer: Add a reset hook that clears the singleton's state in test teardown, or make the instance swappable so each test injects a fresh one.

Singletons are global by design, which is exactly what breaks test isolation. A reset-between-tests hook or a swappable instance restores independence.

How to fix it

1. Add a reset method

Expose a test-only method that resets the singleton's fields to defaults and call it in [TearDown] / before_each, so dirty state never crosses a test boundary.

2. Make the instance swappable

Allow the static instance to be replaced (for example an internal setter) so each test installs a fresh instance and removes it afterward, avoiding hidden coupling entirely.

3. Detect the coupling

Run tests in randomized order; a test that only passes after a specific other test ran is a sign the singleton carried state, pointing you at what to reset.

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.

Reproduce it once with full context and the fix writes itself. The hunt is the expensive part.