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Building beautiful software tests around JUnit

When using Java, it makes sense to build your tests around JUnit. This excerpt from the book Beautiful Code by Alberto Savoia, explains what JUnit is and how developers can use it to test their own code.

The following is an excerpt from Chapter 7, "Beautiful Tests," taken from the book Beautiful Code.


When speaking of beautiful tests, it's hard not to think of the JUnit testing framework. Because I'm using Java, deciding to build my beautiful tests around JUnit was a very easy decision. But before I do that, in case you are not already familiar with JUnit, let me say a few words about it.

JUnit is the brainchild of Kent Beck and Erich Gamma, who created it to help Java developers write and run automated and self-verifying tests. It has the simple, but ambitious, objective of making it easy for software developers to do what they should have done all along: test their own code.

Unfortunately, we still have a long way to go before the majority of developers are testinfected (i.e., have experimented with developer testing and decided to make it a regular and important part of their development practices). However, since its introduction, JUnit (helped considerably by eXtreme Programming and other Agile methodologies, where developer involvement in testing is nonnegotiable) has gotten more programmers to write tests than anything else.* Martin Fowler summed up JUnit's impact as follows: "Never in the field of software development was so much owed by so many to so few lines of code."

JUnit is intentionally simple. Simple to learn. Simple to use. This was a key design criterion. Kent Beck and Erich Gamma took great pains to make sure that JUnit was so easy to learn and use that programmers would actually use it. In their own words:

So, the number one goal is to write a framework within which we have some glimmer of hope that developers will actually write tests. The framework has to use familiar tools, so that there is little new to learn. It has to require no more work than absolutely necessary to write a new test. It has to eliminate duplicate effort.†

The official getting-started documentation for JUnit (the JUnit Cookbook) fits in less than two pages

Here's the key extract from the cookbook (from the 4.x version of JUnit):

When you need to test something, here is what you do:

  1. Annotate a method with @org.junit.Test
  2. When you want to check a value, import org.junit.Assert.* statically, call assertTrue( ), and pass a Boolean that is true if the test succeeds

For example, to test that the sum of two Moneys with the same currency contains a value that is the sum of the values of the two Moneys, write:

    @Test
    public void simpleAdd( ) {
      Money m12CHF= new Money(12, "CHF");
      Money m14CHF= new Money(14, "CHF");
      Money expected= new Money(26, "CHF");
      Money result= m12CHF.add(m14CHF);
      assertTrue(expected.equals(result));
    }

If you have any familiarity with Java, those two instructions and the simple example are all you need to get started. That's also all you need to understand the tests I will be writing. Beautifully simple, isn't it? So, let's get going.

>> Read the complete chapter, "Beautiful Tests."


This was last published in September 2007

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