test(goldens): a custom pumpBeforeTest silently drops the precacheImages default

[marassteiner]

The project wrapper test/helper/golden_test_with_assets.dart:51 exists specifically to default pumpBeforeTest to alchemist.precacheImages:

alchemist.PumpAction pumpBeforeTest = alchemist.precacheImages,

Any golden test that passes its own pumpBeforeTest callback therefore replaces the precaching, not extends it. That is invisible at the call site — the callback looks like an addition, and nothing warns that the wrapper's entire reason for existing has just been switched off for that test.

Current impact: none

Checked for the call sites in test/goldens/screens/support/support_create_ticket_golden_test.dart: the support ticket page and its widgets contain no Image.asset / FadeInImage / SvgPicture, so there is nothing to precache and the baselines are unaffected. This is a latent hazard, not a present defect.

Why it is worth recording

The failure mode is silent and delayed: the first asset image added to a screen whose golden overrides pumpBeforeTest renders blank or flaky in the baseline, and the cause (a callback in a different file, written months earlier) is far from the symptom.

Suggested fix

Compose instead of replace — have the wrapper run alchemist.precacheImages and then the caller's callback, e.g.

pumpBeforeTest: (tester) async {
  await alchemist.precacheImages(tester);
  await callerPumpBeforeTest(tester);
},

so an override cannot drop the default, or document the override semantics in the wrapper's dartdoc.

Context

Surfaced while reviewing #897, which adds such a callback. Pre-existing pattern (several golden tests already override pumpBeforeTest), not a merge blocker for that PR.