typescript-testing-conventions

What problem does it solve? Tests with conditional expect statements can silently pass without running any assertions, hiding real failures and reducing coverage. This Skill provides rules for writing deterministic TypeScript tests that always execute the same assertions and fail fast with clear messages. ## Core Features & Use Cases - Eliminate conditional expects: Replace if-guarded assertions with runtime assert() calls so tests never pass silently when preconditions fail. - Type narrowing in tests: Use assertion utilities like assert and assertIsNonNullable so TypeScript narrows types after checks, keeping tests type-safe. - Deterministic assertions: Ensure every test runs the same number of assertions and fails explicitly when arrays are empty or values are null. - Use Case: When writing a Jest test for a function returning an optional result, assert the result exists before checking its properties, so an unexpected undefined fails the test instead of skipping assertions. ## Quick Start Review my TypeScript test file and rewrite any conditional expect statements to use runtime assertions with proper type narrowing.