Test edge cases and error paths, not just the happy path

Test edge cases and error paths, not just the happy path | BeforeMerge Rules | BeforeMerge

Why this matters

Most bugs hide in boundaries and failures: empty collections, nulls, off-by-one limits, thrown errors, timeouts. A suite that only proves the happy path gives false confidence.

// Bad — only the happy case
it("divides", () => expect(div(6, 2)).toBe(3));
 
// Good — also the error path
it("rejects divide by zero", () => expect(() => div(6, 0)).toThrow(RangeError));

Why This Matters

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Why this matters