TDD (Test Driven Development) feat.Jest

OOP

Object-oriented programming (OOP) is a popular programming paradigm in which code is organized around objects instead of functions. This approach has the added advantage of helping us follow DRY practices.

TDD

Test-driven development (TDD) is the practice of writing tests before writing code. Here's a snapshot of the TDD process:

  • Write a failing test before writing any code.
  • Write the minimal amount of code necessary to make the test pass.
  • Refactor the code to make the test pass.

Jest

  • We can use Jest to test our code.
  • Jest is a testing framework that was created and maintained by Facebook—and it's growing in popularity. Its syntax is easy to understand, and it is extremely popular in Node.js apps.

jest directory structure

  • tests/: contains the tests for the code.
  • fileName.test.js: contains the tests for the fileName.js file. test.js is a convention for test files.
  • Sample test to test fucntion sum of number
describe('sum', () => {
  it('should return the sum of two numbers', () => {
    expect(sum(1, 2)).toBe(3);
  });
});

expect outcome methods

  • any: The any matcher is used to test if a value is anything other than null or undefined.
  • toBe: check result to be equal to expected value.
  • isGreaterThan: check result to be greater than expected value.
  • isLessThan: check result to be less than expected value.
  • toEqual: check result to be equal to expected value.
  • toBeTruthy: check result to be truthy.
  • toBeLessThanOrEqual: check result to be less than or equal to expected value.
  • toBeGreaterThanOrEqual: check result to be greater than or equal to expected value.
  • toBeCloseTo: check result to be close to expected value.
  • toBeInstanceOf: check result to be instance of expected value.
  • toBeNull: check result to be null.
  • toBeUndefined: check result to be undefined.
  • toBeDefined: check result to be defined.
  • toBeNaN: check result to be NaN.
  • toBeFalsy: check result to be falsy.
  • toContain: check result to contain expected value.
  • toMatch: check result to match expected value.
  • toHaveLength: check result to have length of expected value.
  • toHaveProperty: check result to have property of expected value.
  • arrayContaining: check result to contain expected value.

Mock

  • Mocks allow us to fake assumed data, which allows the test at hand to focus only on the logic it cares about.
  • we store mock files in mocks directory.

running test is jest

  • npm run test: run test.
  • npm run test ExampleFileName: run test for ExampleFileName.
  • npm run test -- --watch: run test and watch for changes.
  • npm run test -- --coverage: run test and generate coverage, coverage is a tool that generates a report of the code coverage of your project.

Constructors

  • Constructors are functions that are used to create new objects.
  • we can use new keyword to create new object.
  • the name of the constructor function is preferre to be capitalized. e.g. Person
  • constructor contains all the properties of the object, e.g: A Car
  • this is a reference to the object being created.
  • new keyword is used to create a new object.
function Car(make='', model, year) {
  this.make = make; // will be set to default '' id no make is passed in
  this.model = model;
  this.year = year;
}
let car1 = new Car('Toyota', 'Corolla', 2000);

SOLID Principles

  • Single Responsibility Principle: A class should have a single responsibility.
  • the scope of the function should be limited to the class and contain only the code that is required to perform the task.

Prototype

  • Prototype objects simply inherit the method from the constructor rather than having their own instances of that method.
  • Prototype is a way to share methods and properties between objects.
  • Why use it? We don't want to create a new object for every instance of the class. We want to share the same methods and properties.
  • so we write the function once and then use it in multiple objects.