Flaky Test Prevention

Flaky tests destroy confidence. Quarantine them immediately — fix or delete, never ignore.

Rules:

• Tests MUST NOT share mutable state (each test arranges its own)
• Tests MUST NOT depend on execution order
• Unit tests MUST NOT make real network calls (use fakes or stubs)
• Tests MUST NOT use sleep() or timing-dependent assertions — use deterministic waits or callbacks
• Unit tests MUST NOT produce filesystem side effects (use temp directories, clean up in teardown)
• Tests SHOULD NOT rely on system clock — inject time as a dependency
• If a test fails intermittently, it is broken. It MUST be treated as a P1 bug.

References:

• Martin Fowler: Eradicating Non-Determinism in Tests
• Google Testing Blog: Flaky Tests

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