Running the tester on UNIX based systems (including a mac):
Compile: javac -cp lib/junit-4.12.jar:lib/hamcrest-core-1.3.jar:. DemoArrayImplTester.java
Execute: java -cp lib/junit-4.12.jar:lib/hamcrest-core-1.3.jar:. org.junit.runner.JUnitCore DemoArrayImplTester

Running the tester on Windows systems:
Compile: javac -cp ".;lib\junit-4.12.jar;lib\hamcrest-core-1.3.jar" DemoArrayImplTester.java
Execute: java -cp ".;lib\junit-4.12.jar;lib\hamcrest-core-1.3.jar" org.junit.runner.JUnitCore DemoArrayImplTester