Checking by hand

JavaScript · Unit 20: Testing and debugging

Testing a function doesn't need a separate program: it's calling it with data you know and comparing what came out with what you expected.

That true is your first test.

function double(n) {
  return n * 2;
}
console.log(double(5) === 10);

Prints

true

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. Predict the output
Somebody wrote double in a hurry. What do the two tests print?
2. Complete the code
half(10) should give 5. Complete the test so it prints true.
3. Predict the output
What does this code print?
4. Put the lines in order
Put check(t, got, exp) in order: it prints ok and the test name when what you got equals what you expected, and BAD and the name when it doesn't.
5. Multiple choice
Why is this test useless?
6. Complete the code
The test doesn't match (10 / 2 is 5, not 4). Complete it so the catch picks it up.
7. Predict the output
What does this code print?
8. Find the bug
check should print BAD when what you got isn't what you expected. With 3 * 3 and 6 it prints ok. Which line has the bug?
9. Find the bug
readAge should give back a number and it gives back the text "18". The test says ok anyway. Which line has the bug?
10. Predict the output
Both tests check bigger. What does it print?

It opens in your browser. This lesson is part of the full plan; the first unit of each course is free.