Numbers

Open up the file src/numbers.js in your text editor and take a look inside.

This file contains empty function definitions.

Your challenge is to fill in the function blocks to make the tests pass.

N.B. you can ignore the module.exports keyword for now - this is used to make the functions available outside of the file they are defined it, so that the tests can see them.

Remember you need to find the corresponding test for each function and change the xit to it in order to un-skip it. Head to __tests__/numbers.test.js. We want to find a test that calls our add function. We can see this is actually in the first describe call. Therefore you need to change:

xit('adds the two numbers together', () => {
  ...
})

:bulb:

Note that the ... here shouldn't be typed. It signifies that the code it references is irrelevant in the given context and only the code surrounding it should be changed.

To:

it('adds the two numbers together', () => {
  ...
})

Back in your Terminal, run npm test again. One test should have failed:

Failing test

You can see a few things here:

Expected value to equal: 3 Received: undefined
Comparing two different types of values. Expected number but received undefined.

You can also see an arrow pointing to line 17: expect(add(2, 1)).toEqual(3);

What can you take from this information?

the add function should take two parameters, both numbers.
the return value of the add function should be a number.
when the parameters are 2 and 1, the return value should be 3.

In the body of the add function (back in src/numbers.js), add the following code:

return 3;

Then run the tests again using the same command as before.

You should now see the same failing test at the top but with a new error message - don't worry, just read the new message:

Expected value to equal: 91 Received: 3
an arrow pointing to line 18 - expect(add(15, 76)).toEqual(91);

We now know a bit more about the requirements of the function:

the add function should take two parameters, both numbers.
the return value of the add function should be a number.
when the parameters are 2 and 1, the return value should be 3.
when the parameters are 15 and 76, the return value should be 91.

Looking at the test file (__tests__/numbers.test.js), you can see the full requirements:

expect(add(2, 1)).toEqual(3);
expect(add(15, 76)).toEqual(91);
expect(add(12, 0)).toEqual(12);
expect(add(10, -5)).toEqual(5);

To fix this problem, you're going to have to add a couple of parameters to the function, and use those along with the + arithmetic operator. Edit your add function to look like this (make sure you type the solution, don't just copy and paste!)

const add = (a, b) => {
  return a + b;
};

Arithmetic operators are used to combine two numbers to return a new value. When you're working with numbers in JavaScript, you will normally end up working with these, or the Math object.

If you run the tests again, you should see a big green tick at the top... congratulations! You passed your first ever unit test!

However, there are still 10 more number-based problems for you to solve.

Using the documentation links below and google, solve the remaining number-based problems.

You should only be modifying code inside the src/ folder to make the tests pass - the only changes you should be making in the __tests__ folder is un-skipping tests by changing xit to it.

After you solve each problem, add and commit the changes to git and push them to Github. Once you have solved everything, move onto the next page.

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