Hands on Testing Java: Lab #3

Experiment #1: JUnit Test Case

The JUnit library implements several resources for you to use in testing your programs. In this experiment you will pick up the basics of using JUnit.

The Code

Do this...
Create a test-case class named Experiment01Test.

Everything in Java revolves around classes. Previously, you've seen classes used to implement drivers. For this lab you will create test-case classes. This first experiment will demonstrate what you can (and should) do in a test case class.

Do this...
Run your test-case class.

Keep in mind that this is a test-case class, not a driver---this distinction is very important for running the class properly.

You'll get some output that says that something is wrong: you don't have any actual tests!

This is what it looks like for me in Eclipse:

It will look slightly different in other IDEs and in JUnit's own test runner. However, the basic features are the same.

The big red bar at the top of the window is the "red bar" which indicates that there's a problem.
The failure tab indicates what failed.
The failure trace indicates how it failed.

The failure trace here indicates that there are no tests that are found in the class.

A Test

A test-case class needs to be filled with test methods. "Method" is a technical term in Java which we'll explore in better detail in the next lab; for now, it's just a place to put some testing assertions. Every test method needs to follow this pattern:

test-method pattern

public void testName() {
  assertStatements
}

Name is the name of the specific test.
assertStatements is a list of assert-statements.

So add a test method to Experiments.

Do this...
Add this code inside the Experiment01Test class (i.e., before the very last curly brace):

public void testSimpleAssertions() {

}

The name of the test method (e.g., testSimpleAssertions) should indicate what you're trying to test in the test method.

Do this...
Now you can compile your code, and run it.

Again (and this is the last time you'll be reminded), you're running a test-case class, not a driver!

JUnit will now show you a green bar because your one test passes. Of course, it works because nothing is actually being tested! Actual tests are made with assertions.

Do this...
Add this code inside the curly braces of testSimpleAssertions():

assertEquals("A simple test that 2 equals 2", 2, 2);

Compile, and run the test-case class.

This appears to test (i.e., to assert) that 2 equals 2. That's exactly what it does:

assertion-statement pattern

assertEquals(stringComment, expectedValue, computedValue);

stringComment is a comment about the assertion written as a Java String.
expectedValue is the value you expect to get from the computation being asserted.
computedValue is the computation being asserted.

A Failing Test

You're testing something, and apparently it's working fine. Or is it? Try getting something to fail, like this:

Do this...
Add this assertion statement after the one you just added:

assertEquals("A test that fails", 2, 3);

Now compile, and run the test-case class.

Question #03.01.01 Describe how you can tell that this new assertion statement failed. That is, how does JUnit make it clear that something went wrong?
To be answered in Exercise Questions/lab03.txt.

Do this...
Comment out the assert statement that fails, and then compile, and run the test-case class so that the tester passes its one test.

Observation

%% TODO: too Eclipse specific You now have three places to look for problems.

Compiler errors can be found in the Problems window.
Run-time errors (when running a driver) can be found in the Console window.
Testing errors (when running test-case classes) can be found primarily in the Failure Trace portion of the JUnit window.

Your Own Assertion

Now try an assertion of your own.

Do this...
Add another assertion statement to assert that 1234 is equal to 1234.

Terminology

assert, assertion, driver, test-case class, test method