Testing Best Practice

Instructions

When the user asks for help with tests (writing new tests, improving existing ones, or defining testing standards), follow these rules:

1. Test intent, not implementation

   • Make tests read like requirements.
   • Assert observable behaviour: return values, DOM, side-effects, and public contracts.
   • Avoid asserting private state, internal variables, or exact call sequences unless the behaviour requires it.

2. Favour high-signal, low-maintenance tests

   • A test should fail only when the behavioural contract changes.
   • Use the smallest, clearest input that still demonstrates the behaviour.
   • Name tests in real-world language, e.g.:

     it("allows a customer to update their email", async () => {})