How One Kotlin Keyword Broke Our UI Automation

11 approvals, green tests, and a silent UI failure.

1The Root Cause

A misuse of a Kotlin keyword caused UI automation tests to fail silently. Using apply instead of let led to incorrect test results.

The faulty code was reviewed and approved by 11 different engineers. The code's idiomatic Kotlin appearance masked the error.

While tests remained green, UI components did not contain the correct text. This delayed the detection of the issue.

apply returns the original object, while let returns the result of the block. This difference created a critical error in UI tests.

The applyIf function silently ignored text checks. This caused tests to approve incorrect components.

Replacing apply with letIf ensured correct text checks. This fixed the error.

The API was redesigned to prevent reintroduction of the bug. This ensured similar errors would not compile.

Testing the matchers themselves prevented similar errors. This increased the reliability of the test infrastructure.

11 approvals diffused responsibility. This highlighted the need for more effective code review processes.

This incident emphasized the importance of correct Kotlin scope function usage and continuous testing of test infrastructure.