Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the logic errors pattern
The wrong operator, an inverted condition, a formula the right way round but backwards.
What went wrong: Array.prototype.indexOf() checks strict object equality (===). Passing a new object literal { id } compares different memory references and always returns -1.
The fix: Use findIndex() with a property comparator: users.findIndex(u => u.id === id)
Remember: In JavaScript, indexOf() cannot match objects by structural properties.
The pattern behind it: logic errors.
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