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Testing behaviors

I mentioned in my last post how learning Ruby has made me a better Java developer. In particular, learning RSpec opened my eyes to a new way of unit testing.

RSpec is a library for Ruby that is built around Behavior Driven Development (BDD). In BDD and with RSpec, you focus on specifying the behaviors of a class and write code (tests) that verify that behavior. Whether you do this before you write the class is up to you, but I’ve found that outlining the class’ behaviors before (or while) I write the class helps me figure out what exactly the implementation should do.

You may be thinking that BDD sounds awfully similar to Test Driven Development (TDD). In some ways they are similar: they both encourage writing tests first and for fully testing the code you write. However, TDD doesn’t really guide you into the kinds of tests you should be writing, and I think a lot of people struggle with what they should be testing. BDD attempts to give you this guidance by getting the words right so that you focus on what the behaviors are supposed to be.

Let’s look at an example of a class that represents a playlist. The first step will be to decide what the class should and should not do:


  • should not allow a null name
  • should not allow a blank name
  • should always have a name
  • should allow the name to change
  • should maintain the order of the songs
  • should allow songs to be added
  • should allow songs to be removed
  • should allow songs to be reordered
  • should have a duration that is a summation of the durations of each song
  • should not allow a song to appear more than once

Really, these are just the requirements written as a list. With BDD and JUnit 4.4, we can capture each behavior specification as a single unit test method. Initially, we’ll just stub the methods, but later on we’ll implement the test methods to verify the class actually exhibits that behavior. And since JUnit 4.4 gives us the freedom to name our test methods anything we want, let’s take a play from the RSpec playbook and put these behavior specifications directly in our test method names. Pretty cool! Just start listing the expected behaviors, and the test methods simply fall out:

public class PlaylistTest {
 @Test public void shouldNotAllowANullName() {}
 @Test public void shouldNotAllowABlankName() {}
 @Test public void shouldAlwaysHaveAName() {}
 @Test public void shouldAllowTheNameToChange() {}
 @Test public void shouldMaintainTheOrderOfTheSongs() {}
 @Test public void shouldAllowSongsToBeAdded() {}
 @Test public void shouldAllowSongsToBeRemoved() {}
 @Test public void shouldAllowSongsToBeReordered() {}
 @Test public void shouldHaveADurationThatIsASummationOfTheDurationsOfEachSong() {}
 @Test public void shouldNotAllowASongToAppearMoreThanOnce() {}

By capturing the requirements/behaviors in the test class, we don’t need to document them elsewhere. We can even add JavaDoc if the name isn’t clear. And, with a little work, we could generate that list of requirements by processing (or sequencing!) our code, as long as we follow the convention that the method names form a camel-case but readable English description of the behavior. (In fact, the org.jboss.dna.common.text.Inflector has a method to “humanize” camel-case and underscore-delimited strings, making it a cinch to output human readable code.)

And our test class even compiles. Pretty cool, huh? Oh, and that last requirement that’s not very intuitive? We now have a specification (test method) that verifies the seemingly odd behavior, so if a developer later on changes this behavior, it’ll get caught. (Of course the developer might just blindly change the test, but that’s another problem, isn’t it?)

But back to our development process. At this point, we could implement the test methods using the non-existent Playlist class. It may not compile, but we could then use our IDE to help us create the Playlist class and the methods we actually want. Of course, if this is too weird, you can always stub out the class and then implement the test methods. Personally, I like to implement some of the test methods before going any further, and we’ll use Mockito to stub out a Song implementation.

public class PlaylistTest {
  private Playlist playlist;
  private String validName;
  private Song song1;
  private Song song2;

  public void beforeEach() {
    validName = "Pool party songs";
    playlist = new Playlist();
    song1 = mock(Song.class);
    song2 = mock(Song.class);

  @Test(expected = IllegalArgumentException.class)
  public void shouldNotAllowANullName() {

  @Test(expected = IllegalArgumentException.class)
  public void shouldNotAllowABlankName() {
    playlist.setName("   ");

  public void shouldAlwaysHaveAName() {
    assertThat(playlist.getName(), is("New Playlist"));

  public void shouldAllowTheNameToChange() {
    validName = "New valid playlist name";
    assertThat(playlist.getName(), is(validName));


  public void shouldHaveADurationThatIsASummationOfTheDurationsOfEachSong() {
    assertThat(playlist.getDurationInSeconds(), is(339));
    verify(song1, times(1)).getDurationInSeconds();
    verify(song2, times(1)).getDurationInSeconds();

  public void shouldNotAllowASongToAppearMoreThanOnce() {
    assertThat( playlist.add(song1), is(true));
    assertThat( playlist.add(song2), is(false));

Now we can complete the Playlist class and round out more tests as we discover new requirements and behaviors. Rinse and repeat. And we’ve done it all with just a little convention and JUnit 4.4, meaning it works in our IDE and in our continuous integration system.

The real change that BDD brings is just thinking differently. So while there are some Java frameworks for BDD (e.g., JDave and JBehave), the real benefit comes from changing your testing behavior, not changing your tools.

I hope this long post has inspired you to rethink how you do testing and to give BDD a try. Let us know what you find!


Filed under: techniques, testing, tools

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