What causes a Unity test that passes locally but fails only in CI?

The test depends on a machine-specific default such as the current culture, decimal separator, time zone, or path separator that differs between your workstation and the CI agent.

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 Unity Test That Passes Locally but Fails in CI

Quick answer: Pin culture and time zone inside the test, use invariant formatting for any string comparison, and avoid asserting on environment-derived values.

Tests that compare formatted numbers or dates pass on your en-US machine and fail on a CI agent set to a comma-decimal locale. Forcing invariant culture removes the difference.

How to fix it

1. Force invariant culture in setup

In [SetUp] set CultureInfo.CurrentCulture = CultureInfo.InvariantCulture so 1.5.ToString() does not become 1,5 on a European agent and break the assertion.

2. Compare values, not formatted strings

Assert on the parsed number or the raw object, not its ToString() output. If you must compare text, format both sides with CultureInfo.InvariantCulture explicitly.

3. Normalize paths and time

Use Path.Combine instead of hardcoded slashes and pin DateTime work to UTC. A CI agent in a different time zone will otherwise shift any local-time assertion.

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.

A crash you can name from its stack trace is a crash you can usually fix in minutes.