CASE 01Start here
5− 7 =−2
BOUNDARY BUG
The vanishing inventory
Five items on the shelf. Seven in the cart. Somehow, checkout says yes.
Catch an oversell before it reaches a customer.
THE WORKING EXAMPLE
Choose a failure. Follow the fix.
Three failure modes in one inventory service. Enter a request, inspect Bob’s repair, and verify actual responses.
0 / 3missions explored
CASE 02A little sneaky
+ + +∞
VALIDATION BUG
The infinite stock trick
Place an order for minus two items. Watch the shelf mysteriously refill.
Explore what happens when an input breaks the rules.
CASE 03Think differently
“abc”→NaN
TYPE BUG
The number that wasn’t
Send a word where a number should be. Can the service still keep count?
See why a type assertion is not runtime validation.
A working API with reviewable results.
How it works Run requests against the original and repaired code, then inspect the test evidence. No account or API key needed.