Running the JUnit tests from your IDE (probably built-in).
Calling ExprTest.main() (which just "manually" makes the calls that JUnit would).
If you get a compile-time error about “class junit.framework.TestCase not found”,
you'll need to make sure
(a) you have JUnit .jars downloaded, and
(b) your CLASSPATH includes it.
See how-to-run-junit.html for further instructions.