Each of the following exercises requires you to write unit tests INSTEAD of the actual program.

In each exercise, the function is already written for you: you get its description, but not its code. Your job is to write assert_equal tests that check whether the function does what the description says. Don’t write the function yourself: your tests must call the one that is provided.

How your tests are graded

When you submit, your tests run several times:

• once against each genuine (correct) version of the function: every one of your tests must pass;
• once against each of a few impostors (incorrect versions): for each of them, at least one of your tests must fail.

You never see these versions. To catch every impostor, your tests need to cover every case the description mentions: normal cases, edge cases, and the inputs the description says to reject. The feedback tells you which of your tests fail on a genuine version, and describes the mistake of each impostor your tests don’t catch yet.

Trying your tests

The function is only there when you submit. You can still run your code in the sandbox (To sandbox, then Run), but there it only lists your tests: it can’t tell you whether they pass.