junit Tests Unit testing using JUnit


Here we have a class Counter with methods countNumbers() and hasNumbers().

public class Counter {

    /* To count the numbers in the input */
    public static int countNumbers(String input) {
        int count = 0;
        for (char letter : input.toCharArray()) {
            if (Character.isDigit(letter))
        return count;

    /* To check whether the input has number*/
    public static boolean hasNumber(String input) {
        return input.matches(".*\\d.*");

To unit test this class, we can use Junit framework. Add the junit.jar in your project class path. Then create the Test case class as below:

import org.junit.Assert; // imports from the junit.jar
import org.junit.Test;

public class CounterTest {

    @Test // Test annotation makes this method as a test case
    public void countNumbersTest() {
        int expectedCount = 3;
        int actualCount = Counter.countNumbers("Hi 123");
        Assert.assertEquals(expectedCount, actualCount); //compares expected and actual value

    public void hasNumberTest() {
        boolean expectedValue = false;
        boolean actualValue = Counter.hasNumber("Hi there!");
        Assert.assertEquals(expectedValue, actualValue);

In your IDE you can run this class as "Junit testcase" and see the output in the GUI. In command prompt you can compile and run the test case as below:

\> javac -cp ,;junit.jar CounterTest.java
\> java  -cp .;junit.jar org.junit.runner.JUnitCore CounterTest

The output from a successful test run should look similar to:

JUnit version 4.9b2
Time: 0.019

OK (2 tests)

In the case of a test failure it would look more like:

Time: 0.024
There was 1 failure:
1) CountNumbersTest(CounterTest)
java.lang.AssertionError: expected:<30> but was:<3>
... // truncated output
Tests run: 2,  Failures: 1