Pre-submit UI Tests at Pinterest

Pinterest's UI test suite was failing more than 50% of the time. Engineers were drowning in false positives, and tests had lost all credibility.

Pinterest's mobile team moved their entire end-to-end UI test suite from post-submit to pre-submit, running 300 tests on every code change. This meant solving hard problems around speed, cost, flakiness, and developer experience.

Key Takeaways

• Pass rate jumped from under 50% to over 90% after the shift
• Every test requires an owner and silenced tests must be fixed within 2 weeks
• Smart sharding and custom schedulers keep 300 tests under 30 minutes
• Result caching lets devs skip reruns when tests are false negatives
• Stability Enforcer auto-silences tests showing over 20% flakiness

The article reveals their phased rollout strategy and the surprising infrastructure challenges they hit when parallelizing tests across Firebase and AWS.