01. Introduction to Unit Testing

Unit Testing

Testing is important because programming is hard, and because debugging programs is harder. Good unit tests:

• Let you know if you broke something.
• Make it clear what the program is supposed to do.

**Unit Test: **A piece of code that verifies the one behavior of another piece of code.

• Each behavior your application performs should have its own unit test.
• Each unit test should verify one behavior.

App.java

public class App {
    public int addTwoNumbers(int x, int y) { 
        return x + y; 
    }
}

This method adds two numbers together. To test that method does what it's supposed to do, you could write a method like this:

    public void testAddTwoNumbers() {
        int input1 = 5;
        int input2 = 6;
        int expected = 11;
        int result = addTwoNumbers(input1, input2);
        if(expected != result) {
            throw new RuntimeException(String.format(
                "addTwoNumbers expected %d but returned %d for inputs %d, %d",
                expected, result, input1, input2));
        } else {
            System.out.println("addTwoNumbers Pass");
        }
    }