Learn JavaScript Unit Testing

Question 1

Write Good Tests With Mocha

before() Hooks

Answer 1

In a test file, the function before() will be executed first, regardless of it’s placement in the code block. before() is often used to set up code, like variables and values, for other function calls to use in their execution.

before(() => {
   path = './message.txt';
 });

Question 2

Write Good Tests With Mocha

beforeEach() Hook

Answer 2

In a test file, the function beforeEach() will be executed before each test. beforeEach() is often used to set up or reset code, like variables and values, for other function calls to use in their execution.

beforeEach(() => {
   testCounter++;
 });

Question 3

Write Good Tests With Mocha

after() Hooks

Answer 3

In a test file, the function after() will be executed last, regardless of its placement in the code block. after() is often used to print out results from the tests that were run in the suite or to reset variables and values.

after(() => {
   console.log(""number of tests: "" + testCounter);
 });

Question 4

Write Good Tests With Mocha

afterEach() Hooks

Answer 4

In a test file, the function afterEach() will be executed after each test. afterEach() is often used to print out results from a particular test that was run in the suite or to reset variables and values.

afterEach(() => {
   path = './message.txt';
 });

Question 5

Write Good Tests With Mocha

Test Frameworks

Answer 5

Test frameworks are used to organize and automate tests that provide useful feedback when errors occur.

Question 6

Write Good Tests With Mocha

describe() functions

Answer 6

In Mocha, the describe() function is used to group tests. It accepts a string to describe the group of tests and a callback function which contains it() tests. Calls to describe() are commonly nested to resemble the structure of the code being tested.

describe('group of tests', () => {
  //Write it functions here
  
});

Question 7

Write Good Tests With Mocha

it() functions

Answer 7

In Mocha, the it() function is used to execute individual tests. It accepts a string to describe the test and a callback function to execute assertions. Calls to it() are commonly nested within describe() blocks.

describe('+', () => {
  it('returns the sum of its arguments', () => {
    // Write assertions here
    
  });
});

Question 8

Write Good Tests With Mocha

The assert Library

Answer 8

The assert library is used to make assertions. It contains numerous functions that enable the tester to write easily readable assertions and throw AssertionErrors within a test.

describe('+', () => {
  it('returns the sum of its arguments', () => {
    // Write assertion here
    assert.ok(3 + 4 === 7)
  });
});

Question 9

Write Good Tests With Mocha

assert.ok()

Answer 9

The assert.ok() function is be used to evaluate a boolean expression within a test. If the expression evaluates to false, an AssertionError is thrown.

describe('+', () => {
  it('returns the sum of its arguments', () => {
    // Write assertion here
    assert.ok(3 + 4 === 7)
  });
});

Question 10

Write Good Tests With Mocha

Setup Phase

Answer 10

In testing, the Setup phase is where objects, variables, and set conditions that tests depend on are created.

Question 11

Write Good Tests With Mocha

Exercise Phase

Answer 11

In testing, the Exercise phase is where the functionality under test is executed.

Question 12

Write Good Tests With Mocha

Verify Phase

Answer 12

In testing, the Verify phase is where expectations are checked against the result of the exercise phase. assert would be used here.

Question 13

Write Good Tests With Mocha

Teardown Phase

Answer 13

In testing, the Teardown phase is where the environment is reset before the next test runs. The teardown phase ensures that a test is isolated from other tests.

Question 14

Write Good Tests With Mocha

Tests in Isolation

Answer 14

A project’s tests should run in isolation from one another. One test shouldn’t affect another. Tests should be able to run in any order.

Question 15

Write Good Tests With Mocha

assert.equal()

Answer 15

assert.equal() verifies a loose equality (==) comparison. Using assert.equal() is more expressive, it’s more clear that it’s verifying equality than assert.ok().

Question 16

Write Good Tests With Mocha

assert.strictEqual()

Answer 16

assert.strictEqual() verifies a strict equality (===) comparison.

const a = 3;
const b = '3';
assert.equal(a, b);
assert.strictEqual(a, b);

Question 17

Write Good Tests With Mocha

assert.deepEqual()

Answer 17

assert.deepEqual() compares values within two objects. It will compare the values using loose (==) equality.

const a = {relation: 'twin', age: '17'};
const b = {relation: 'twin', age: '17'};

assert.strictEqual(a, b);

Question 18

Write Good Tests With Mocha

Why Test?

Answer 18

Testing can catch and identify issues with your implementation code before you deploy it to users