How to Fix an Edit-Mode Test Calling Play-Mode-Only APIs in Unity

Edit-mode tests execute in the editor without a play loop, so anything that depends on frames, physics, or MonoBehaviour lifecycle silently does nothing or throws. Splitting the test by what it actually needs is the fix.

How to fix it

1. Decide which loop the test needs

If the code under test reads Time.deltaTime, steps physics, runs a coroutine, or relies on Awake/Start, it must be a play-mode test. Pure functions and data transforms belong in edit-mode tests.

2. Put the test in the right assembly

Create a play-mode test assembly (an asmdef with Test Assemblies set and no Editor platform restriction) and move the offending test there. Edit-mode tests live in an editor-only test asmdef.

3. Use UnityTest for frame-dependent assertions

In play mode, mark the method [UnityTest] and return IEnumerator so you can yield return null to advance frames before asserting. A plain [Test] never advances the loop.

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 Unity 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.