Barebones Guide to JUnit on the Command Line

Introduction

JUnit is a testing framework for Java. It is primarily aimed for IDEs, but with some perseverance it can be used on the command line.

ConsoleLauncher

You will need ConsoleLauncher, a java executable, to run JUnit from the command line. At time of writing the latest version is junit-platform-console-standalone-1.6.0.jar and can be downloaded from the Maven Repository. Download this file to your working directory.

Create a sample java file

Using your text editor of choice create a file called SampleUnit.java and copy and paste the following code in it:

public class SampleUnit {

    public int addInts(int a, int b){
        return a + b;
    }

    public boolean validAboveZero(int a) {
        if (a>0) {
            return true;
        }
        return false;
    }
}

Create a sample test file

Creating a file called SampleUnitTest.java copy the following:

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
import static org.junit.Assert.assertEquals;
import org.junit.Test;

public class SampleUnitTest {

    @Test
    public void testAddInts() {
        SampleUnit sampleUnit = new SampleUnit();
        int result = sampleUnit.addInts(2, 2);
    // The below should fail.
        assertEquals("Not adding correctly!", 5, result);
    }

    @Test
    public void testValidAboveZero() {
        SampleUnit sampleUnit = new SampleUnit();
        boolean result = sampleUnit.validAboveZero(2);
        assertTrue(result);
    }

    @Test
    public void testValidFail() {
        boolean result = false;
        assertFalse(result);
    }
}

Compile

Run the following from the command line:

javac SampleUnit.java
javac -cp junit-platform-console-standalone-1.6.0.jar:. SampleUnitTest.java

This assumes the JUnit jar, SampleUnit.java and SampleUnitTest.java are all in the same directory. The compiler will create two new files: SampleUnit.class and SampleUnitTest.class.

Run the tests

Finally at the command line run:

java -jar junit-platform-console-standalone-1.6.0.jar --class-path . -c SampleUnitTest

This should output something like this:

Thanks for using JUnit! Support its development at https://junit.org/sponsoring

╷
├─ JUnit Jupiter ✔
└─ JUnit Vintage ✔
   └─ SampleUnitTest ✔
      ├─ testAddInts ✘ Not adding correctly! expected:<5> but was:<4>
      ├─ testValidFail ✔
      └─ testValidAboveZero ✔

Failures (1):
  JUnit Vintage:SampleUnitTest:testAddInts
    MethodSource [className = 'SampleUnitTest', methodName = 'testAddInts', methodParameterTypes = '']
    => java.lang.AssertionError: Not adding correctly! expected:<5> but was:<4>
       org.junit.Assert.fail(Assert.java:89)
       org.junit.Assert.failNotEquals(Assert.java:835)
       org.junit.Assert.assertEquals(Assert.java:647)
       SampleUnitTest.testAddInts(SampleUnitTest.java:13)
       java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
       java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
       java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
       java.base/java.lang.reflect.Method.invoke(Method.java:566)
       org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
       org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
       [...]

Test run finished after 43 ms
[3 containers found]
[0 containers skipped]
[3 containers started]
[0 containers aborted]
[3 containers successful]
[0 containers failed]
[3 tests found]
[0 tests skipped]
[3 tests started]
[0 tests aborted]
[2 tests successful]
[1 tests failed]

ConsoleLauncher Options Frustration

The ConsoleLauncher has an extensive list of command line options for providing arguments. Above I’ve gone for --class-path . -c SampleUnitTest defined respectively as:

-cp, --classpath, --class-path=PATH[;|:PATH...] Provide additional classpath entries -- for example, for adding engines and their dependencies. This option can be repeated.
-c, --select-class=CLASS Select a class for test discovery. This option can be repeated.

Why these two specifically? A simple reason - after a couple of hours reading stack overflow and trying various random combinations, it appears to be the only option I could get to work. This may be due to my incompetence, my setup (openjdk 11.0.6) or a bug.