james-demiraiakian/03-functions-tdd

Testing Functions with TDD

Review core JavaScript syntax and context through testing functions

QUnit built-ins

Our tests.js file has access to a new built-in, QUnit and we will be using the QUnit.test method which will be assigned to a test variable.

We will also be using the expect built-in that will be passed to our testing function

The test

The structure of a test is very similar to the use of addEventListener!

// only once at top of file:
const test = QUnit.test;

// Each test case
test('test name', (expect) => {

});

Part	Purpose
test	Built-in QUnit testing method
'test name'	Descriptive test name
(expect) => {...}	Function (arrow function) that will be called by qUnit to run the test

Test setup

test('demo: adds two numbers', (expect) => {
    //Arrange
    // Set up your arguments and expectations (inputs and outputs)
    const x = 2;
    const y = 5;
    const expected = 7;

    //Act 
    // Call the function you're testing and set the result to a const
    const actual = add(x, y);

    //Expect
    // Make assertions about what is expected versus the actual result
    expect.equal(actual, expected);
});

Part	Purpose
// Arrange	What are the inputs and outputs?
// Act	Run the function being tested!
// Assert	Validate by asserting something is true

Functions

Write your tests and corresponding functions one feature at a time. Don't stub out all the functions and imports!

Exporting a function

Add the export keyword in front of your declared function definition:

export function add(x, y) {
    return x + y;
}

Importing function(s)

Use the following syntax to import the functions from the other file:

import {
    add,
    subtract,
    areaOfTriangle,
} from './functions.js';

Process

For each function feature:

1. Read description, ask questions if not understood
2. Identify function inputs and output
3. Identify number of test cases required
4. Start with first test
5. Decide on name for test and for function
6. Add empty test in tests.js
7. Create and export empty function in functions.js and import into tests.js
8. Write test:
   • Translate inputs and outputs into "Arrange" variables,
   • write the "Act" function call
   • modify "Assert" if needed
9. Add parameters to function, write code to make pass
10. Implement additional tests if required (using same function)