System Rules on the Command Line

Introduction

This is a more of a follow up to my previous post Barebones Guide to JUnit on the Command Line rather than an entirely new topic. System Rules is a “a collection of JUnit rules for testing code that uses java.lang.System” - in other words a way to use JUnit to test for cases where you want to use a System.out.print or similar. The majority of the documentation is how to integrate it with an IDE, this is a quick reference on how to use it at the Linux command line. At time of writing I’m using Ubuntu 18.04.4 LTS and OpenJDK 11.0.6.

Download relevant Java Archive (JAR) files

You will need to place junit-platform-console-standalone-1.6.0.jar and system-rules-1.19.0.jar in your current working directory. These can be downloaded from JUnit Maven repo and Get System Rules respectively. The repo at JUnit isn’t particularly human readable (just a long list of files), so make sure you download the correct one. There may be later versions by the time you read this.

Create a sample java file

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

public class SystemOut {
    public void PrintToSystem(boolean input) {
        if (input) {
            System.out.print("Hello from PrintToSystem.");
        }
    }
}

Create a sample test file

Creating a file called SystemOutTest.java copy the following:

import static org.junit.Assert.assertEquals;
import org.junit.contrib.java.lang.system.SystemOutRule;
import org.junit.Test;
import org.junit.Rule;

public class SystemOutTest {
    @Rule
    public SystemOutRule systemOutRule = new SystemOutRule().enableLog();

    @Test
    public void testPrintToSystem() {
        SystemOut systemOut = new SystemOut();
        systemOut.PrintToSystem(true);
        assertEquals("Hello from PrintToSystem.", systemOutRule.getLog());
    }
}

Compile

Run the following from the command line:

javac SystemOut.java
javac -cp .:junit-platform-console-standalone-1.6.0.jar:system-rules-1.19.0.jar SystemOutTest.java

This assumes all files are in the same directory. The compiler will create two new class files.

Run the tests

Finally at the command line run:

java -jar junit-platform-console-standalone-1.6.0.jar --class-path .:system-rules-1.19.0.jar -c SystemOutTest

This should output:

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

╷
├─ JUnit Jupiter ✔
└─ JUnit Vintage ✔
   └─ SystemOutTest ✔
      └─ testPrintToSystem ✔

Test run finished after 42 ms
[3 containers found]
[0 containers skipped]
[3 containers started]
[0 containers aborted]
[3 containers successful]
[0 containers failed]
[1 tests found]
[0 tests skipped]
[1 tests started]
[0 tests aborted]
[1 tests successful]
[0 tests failed]

Conclusion

We’re done. If this helped, or you have a pickup, please comment below.