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TRACK 07

Testing

You write the tests, not the code. Every suite is run against deliberately broken implementations, and scored on the bugs it catches.

6 challenges3 free2h of build time6 graded by running your code
Before you start

No prior testing experience is assumed anywhere in this track — most developers arrive having never written a test, and the hints are written for that rather than as reminders. If you can read a JavaScript function, you can start here.

Tests That Catch Bugs

Write the tests, not the code. Your suite is graded on the bugs it catches.

  1. Your first real testOne assertion is not a test suite. Prove it.Beginner · 10 min
  2. The cases nobody writesEmpty, single, negative, fractional. Where production actually breaks.Beginner · 12 min
  3. One either sideOff-by-one is the most common bug there is. Test on the line and both sides of it.Beginner · 12 min
  4. Testing what you cannot seeThe function returns nothing. Observe what it did instead.Intermediate · 18 min · Pro
  5. The failure pathTesting the throw. And the forgotten await that makes every test pass.Intermediate · 18 min · Pro
  6. Rules, not examplesSome bugs no example finds. Assert the properties that must always hold.Advanced · 22 min · Pro