Writing tests

JavaScript · Unit 20: Testing and debugging

Full plan
JavaScript
10 exercises

A test suite is a list of checks, each with its own name and each looking at one single thing.

That's the rule: one test, one idea. Here there are three ideas about isEven, and each one reads on its own.

function check(t, got, exp) {
  const r = got === exp ? "ok" : "BAD";
  console.log(r + " " + t);
}
function isEven(n) {
  return n % 2 === 0;
}
check("even", isEven(4), true);
check("odd", isEven(7), false);
check("zero", isEven(0), true);

Prints

ok even
ok odd
ok zero

The rest of the explanation is in the lesson, which is part of the full plan.

Exercises in this lesson

You do them in the app, which checks them on the spot and explains why.

1. Multiple choice
clean strips spaces and lowercases. If this test prints BAD, what do you know?
2. Predict the output
The same two ideas, now as two tests. What does it print?
3. Complete the code
cut keeps the first three letters. Complete what you expect from a two-letter text.
4. Predict the output
evens really does return [2, 4]. What do the two tests print?
5. Complete the code
Complete it so same compares the contents of both arrays.
6. Put the lines in order
Put together a check that works for arrays too: turn both sides into text and then decide the word.
7. Find the bug
Both tests check the same length and both should print ok. The second one prints BAD. Which line has the bug?
8. Multiple choice
isAdult(n) says whether n is 18 or more. You already tried 17 and 25. Which test is missing?
9. Predict the output
card builds a record with three properties. What do the tests print?
10. Predict the output
Both objects hold the same data. What does it print?

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