Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the scope and closure bugs pattern
Every callback reports the last value, a counter never increments, UnboundLocalError on a variable you can see.
What went wrong: the code uses fee one line before it is created.
The fix: put const fee = 5; first, then const total = base + fee;
Remember: create a variable before you use it. The error message tells you which one.
The pattern behind it: scope and closure bugs.
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<iframe src="https://trybughunt.com/embed/7cdf9d9e-297e-4d8e-9674-91fc53a7188a" title="Debugging challenge: Adding a fee crashes before the fee exists" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe>
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