# Exercises: Unit Testing

In many of your previous coding tasks, you had to verify that your code worked before moving to the next step. This often required you to add `console.log()` statements to your code to check the value stored in a variable or returned from a function. This approach finds and fixes syntax, reference, or logic errors AFTER you write your code.

In this chapter, you learned how to use unit testing to solve coding errors. Even better, you learned how to PREVENT mistakes by writing test cases before completing the code. The exercises below offer practice with using tests to find bugs, and the studio asks you to implement TDD.

For the exercises, open `javascript-projects/unit-testing/exercises` to find the files you will need to get started.

## Automatic Testing to Find Errors

Let’s begin with the following code in `checkFive.js`:

 `````` 1 2 3 4 5 6 7 8 9 10 11 12 `````` `````` function checkFive(num){ let result = ''; if (num < 5){ result = num + " is less than 5."; } else if (num === 5){ result = num + " is equal to 5."; } else { result = num + " is greater than 5."; } return result; } ``````

The function checks to see if a number is greater than, less than, or equal to 5. We do not really need a function to do this, but it provides good practice for writing test cases.

Note that the `exercises` directory also contains a `tests` directory for us.

1. We need to add a few lines to `checkFive.js` and `checkFive.test.js` to get them to talk to each other.

1. `checkFive.test.js` needs to access `checkFive.js`. Add a `require` statement to accomplish this.

2. Make the `checkFive` function available to the spec file, by using `module.exports`.

2. Set up your first test for the `checkFive` function. In the `checkFive.test.js` file, add a `describe` function with one `test` clause:

 ``````1 2 3 4 5 6 7 8 9 `````` `````` const checkFive = require('../checkFive.js'); describe("checkFive", function(){ test("Descriptive feedback...", function() { //code here... }); }); ``````
3. Now write a test to see if `checkFive` produces the correct output when passed a number less than 5.

1. First, replace `Descriptive feedback...` with a DETAILED message. This is the text that the user will see if the test fails. Do NOT skimp on this. Refer back to Specifications and Expectations section to review best practices.

2. Define the variable `output`, and initialize it by passing a value of `2` to `checkFive`.

 ``````1 2 3 4 5 6 7 8 9 `````` `````` const checkFive = require('../checkFive.js'); describe("checkFive", function(){ test("Descriptive feedback...", function(){ let output = checkFive(2); }); }); ``````
3. Now use the `expect` function to check the result:

 `````` 1 2 3 4 5 6 7 8 9 10 `````` `````` const checkFive = require('../checkFive.js'); describe("checkFive", function(){ test("Descriptive feedback...", function(){ let output = checkFive(2); expect(output).toEqual("2 is less than 5."); }); }); ``````
4. Run the test script and examine the results. The test should pass.

5. Now change line 3 in `checkFive.js` to `if (num > 5)` and rerun the test.

6. Change line 3 back.

4. Add two more `test` clauses inside `describe`—one to test what happens when `checkFive` is passed a value greater than 5, and the other to test when the value equals 5.

## Try One on Your Own

Time for Rock, Paper, Scissors! The function in `RPS.js` takes the choices (`'rock'`, `'paper'`, or `'scissors'`) of two players as its parameters. It then decides which player won the match and returns a string.

 `````` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 `````` `````` function whoWon(player1,player2){ if (player1 === player2){ return 'TIE!'; } if (player1 === 'rock' && player2 === 'paper'){ return 'Player 2 wins!'; } if (player1 === 'paper' && player2 === 'scissors'){ return 'Player 2 wins!'; } if (player1 === 'scissors' && player2 === 'rock '){ return 'Player 2 wins!'; } return 'Player 1 wins!'; } ``````
1. Set up the `RPS.js` and `RPS.spec.js` files to talk to each other.

2. Write a test in `RPS.test.js` to check if `whoWon` behaves correctly when the players tie (both choose the same option). Click “Run” and examine the output. SPOILER ALERT: The code for checking ties is correct in `whoWon`, so the test should pass. If it does not, modify your `test` statement.

3. Write tests (one at a time) for each of the remaining cases. Run the tests after each addition, and modify the code as needed. There is one mistake in `whoWon`. You might spot it on your own, but try to use automated testing to identify and fix it.

## Bonus Mission

What if something OTHER than `'rock'`, `'paper'`, or `'scissors'` is passed into the `whoWon` function? Modify the code to deal with the possibility.

Don’t forget to add another `test` clause in `RPS.test.js` to test for this case.