What is unit testing?

Unit testing is the process of testing the smallest isolated part of a program, called a unit (module or component), to confirm that it functions as expected.

• Purpose: To verify the correctness of an individual module.
• Advantages:
  • Early detection of errors.
  • Improved code quality.
  • Facilitation of refactoring.
  • Documentation of code functionality.
• Tools: JUnit, Mockito, PowerMock (for Java).
• Principle: Writing test cases that check specific functionality of a unit by providing certain data as input and verifying the expected result or behavior.
• Characteristics of good unit tests:
  • Independence: Tests do not depend on each other.
  • Automation: Can be executed automatically.
  • Speed: Execute quickly.
  • Repeatability: Yield the same result every time.
  • Isolation: Test only the tested unit, not its dependencies (using mocks).

Example with JUnit:

// Class we want to test
public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }
}

// Example of a unit test with JUnit
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class CalculatorTest {

    @Test
    void testAddPositiveNumbers() {
        Calculator calculator = new Calculator();
        int result = calculator.add(2, 3);
        assertEquals(5, result, "Sum of positive numbers should be correct");
    }

    @Test
    void testAddZero() {
        Calculator calculator = new Calculator();
        int result = calculator.add(0, 5);
        assertEquals(5, result, "Sum with zero should be correct");
    }
}