This section will describe how to use the JUnit framework to create and run tests against your developed classes. JUnit was initially created by Erich Gamma and Kent Beck. JUnit has evolved throughout the years and its latest incarnation is JUnit 5 which we will be describing in this section.

Minimial Test

While JUnit 5 contains a really good User Guide. We will only give enough information here to get you started with this framework. Let us then look at how we can create a test the following Point class.

package org.example;

public class Point {

    private int x, y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int getX() { return x; }
    public int getY() { return y; }

    public void setX(int x) { this.x = x; }
    public void setY(int y) { this.y = y; }
}

The first thing that one should consider when creating tests is what is a good pattern to follow? You should create the test class using the same package as the class that you are testing. Thus a test class for the Point can be defined as.

package org.example;

import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.Assertions;

public class PointTest {

    @BeforeAll
    static void beforeAll() {
        ...
    }

    @AfterAll
    static void afterAll() {
        ...
    }

    @BeforeEach
    void beforeEach() {
        ...
    }

    @AfterEach
    void afterEach() {
        ...
    }

    @Test
    void testOne() {
        Point point = new Point(1,2);

        Asserions.assertEqual(point.getX(), 1);
        Asserions.assertEqual(point.getY(), 1);
    }

    @Test
    void testTwo() {
        Assertions.fail("This is a failed test");
        ...
    }

    // Helper methods.
    private Point create(int x, int y) {
        return new Point(x,y);
    }

    ...

}

The above test should offer enough to be able to get started when writing tests using the JUnit 5 framework. The JUnit 5 framework uses the Assertions class methods to determine if the given tests are successful or not. These methods will generate an exception if the given conditional test is incorrect. The generated exception will contain information about the discrepency of the test by describing what is expected and what was the actually produced.

We now explain the anatomy of the above test. The references with the preceeding @ sign are called annotations and this is used by the JUnit framework to determine how those methods should be called. The ones that contain the BeforeAll and AfterAll annotations will be executed before and after all test methods that have been defined. While the ones that contain the BeforeEach and AfterEach annotations will be executed before and after each defined test. While the ones with the Test annotations are actually the tests that will be executed. Finally, the above test class contains methods that are not called by the JUnit framework but that are used by the test for whatever needs it is required. This just shows that one doesn’t need to only define methods that are annotated with the JUnit framework annotations.

Conditional Test Annotations

This section will expand on the features that are part of the JUnit test framework. We will take a look at how one can go about running tests given different conditional requirements that you can easily implement. Let us then look at how we can use the EnableIf annotation. Let us then add an EnabledIf check to the PointTest

package org.example;

import org.junit.jupiter.api.Test;
...
import org.junit.jupiter.api.condition.EnableIf;

public class PointTest {

    public boolean condition() {
        ...
    }

    @EnabledIf("condition")
    @Test
    public void test() {
        ...
    }
}

The above use of the EnabledIf conditional test annotation will determine if the given test method will be executed or not depending on the condition method return statement. Note that the condition method will return a boolean value. This is a requirement for the use of the EnabledIf conditional test annotation. This also the case with the DisabledIf conditional test annotation. This above was a simple implementation of one of the different conditional test annotations that the JUnit5 test framework contains. There are other conditional test annotations that are avaliable at Conditional Test Annotations.

Conclusion

While the JUnit Test, BeforeEach, AfterEach, BeforeAll and AfterAll annotations and the Assertions class should suffice to get start with the JUnit 5 framework. There are other annotations and assertions that one can use at the following JUnit Javadoc link or one can look at the JUnit User Guide.