public class Calculator {

private Calculator calculator = new Calculator();

public double multiply(double a, double b) { return a * b; }

// src/main/java/com/example/App.java

package com.example;

// src/test/java/com/example/CalculatorTest.java

package com.example;

calculator/ ├── pom.xml └── src ├── main │ └── java │ └── com │ └── example │ └── App.java └── test └── java └── com └── example └── AppTest.java Let's add a feature to our calculator application that allows it to perform addition, subtraction, multiplication, and division. 3.1 Create a Calculator Class Create a new Java class Calculator.java in src/main/java/com/example :

// src/main/java/com/example/Calculator.java

public double subtract(double a, double b) { return a - b; }

@Test void testSubtract() { assertEquals(5, calculator.subtract(10, 5), "Subtraction failed"); }

@Test void testAdd() { assertEquals(15, calculator.add(10, 5), "Addition failed"); }

@Test void testDivide() { assertEquals(2, calculator.divide(10, 5), "Division failed"); }

public double add(double a, double b) { return a + b; }

package com.example;