Unit Testing Explained

Key Concepts

Unit testing is a software testing method where individual units or components of a software are tested. The key concepts include:

• Definition and Purpose
• Test Frameworks
• Test Cases
• Assertions
• Mocking
• Test Coverage

Definition and Purpose

Unit testing involves testing individual components of the software to ensure they work as expected. The purpose is to isolate each part of the program and show that the individual parts are correct.

Test Frameworks

Test frameworks provide the necessary tools and libraries to write and run unit tests. Popular JavaScript frameworks include Jest, Mocha, and Jasmine.

// Example using Jest
describe('sum', () => {
    test('adds 1 + 2 to equal 3', () => {
        expect(sum(1, 2)).toBe(3);
    });
});
    

Test Cases

Test cases are specific scenarios that are tested to ensure the code behaves as expected. Each test case should be independent and cover a specific functionality.

// Example of a test case
test('should return the correct sum', () => {
    expect(sum(1, 2)).toBe(3);
    expect(sum(-1, 1)).toBe(0);
    expect(sum(0, 0)).toBe(0);
});
    

Assertions

Assertions are statements that check whether a condition is true. If the condition is false, the test fails. Assertions are used to validate the expected behavior of the code.

// Example of assertions
expect(sum(1, 2)).toBe(3);
expect(sum(-1, 1)).not.toBe(1);
    

Mocking

Mocking is a technique where mock objects are used to simulate the behavior of real objects in a controlled way. This is useful for isolating the code under test.

// Example of mocking using Jest
jest.mock('./math', () => ({
    sum: jest.fn(() => 3)
}));

test('mocked sum function', () => {
    expect(sum(1, 2)).toBe(3);
});
    

Test Coverage

Test coverage is a measure of how much of the code is executed by the test cases. High test coverage indicates that a larger portion of the code is tested, reducing the likelihood of undetected bugs.

// Example of test coverage report
Statements   : 90%
Branches     : 85%
Functions    : 100%
Lines        : 90%
    

Examples and Analogies

Imagine unit testing as a quality control process in a factory:

• Definition and Purpose: Each part of a product is tested individually to ensure it meets quality standards.
• Test Frameworks: The tools and machinery used to perform the tests.
• Test Cases: Specific scenarios or conditions that each part must pass to be considered functional.
• Assertions: The criteria that determine if a part is acceptable or needs to be reworked.
• Mocking: Using substitute parts to test the main part without relying on other components.
• Test Coverage: The percentage of parts that have been tested, ensuring comprehensive quality control.