How to write a Sample program to use junit-4.8.1.jar?

JUnit is a simple framework to write repeatable tests for Java applications. In order to use junit-4.8.1.jar, we need to write a simple Java application, Calculator.java:

// Copyright (c) 2015 FYIcenter.com
public class Calculator {
  public int evaluate(String expression) {
    int sum = 0;
    for (String summand: expression.split("\\+"))
      sum += Float.valueOf(summand);
    return sum;
  }
}

This sample Java program is simple. But it does have some issues:

• It does not support substraction well.
• It does not support numbers with fractions well.

Let's write JUnit test program, CalculatorTest.jar, to show those issues:

// Copyright (c) 2015 FYIcenter.com
import junit.framework.TestCase;
public class CalculatorTest extends TestCase {
  public void testAddition() {
    Calculator calculator = new Calculator();
    int sum = calculator.evaluate("1+2+3");
    assertEquals(6, sum);
  }
  public void testFraction() {
    Calculator calculator = new Calculator();
    int sum = calculator.evaluate("2.4+2.6");
    assertEquals(5, sum);
  }
  public void testSubtraction() {
    Calculator calculator = new Calculator();
    int sum = calculator.evaluate("10-1");
    assertEquals(9, sum);
  }
}

This sample program, CalculatorTest.java, does the following:

• It uses @Test annotation to identify a test method.
• It uses static JUnit method assertEquals() to perform an equal assertion.

Of course, you need to compile them with JDK to make them ready to run:

\fyicenter>java -version
java version "1.8.0_45"

\fyicenter>javac Calculator.java

\fyicenter>javac -cp .;\local\lib\junit-4.8.1.jar CalculatorTest.java

Note that you need to provided junit-4.8.1.jar in the classpath to compile CalculatorTest.java

Back to FAQ for JUnit (Java Unit) Testing.