JUnit 4.4 변경내용

Summary of Changes in version 4.4

JUnit is designed to efficiently capture developers' intentions about their code, and quickly check their code matches those intentions. Over the last year, we've been talking about what things developers would like to say about their code that have been difficult in the past, and how we can make them easier.

assertThat

Two years ago, Joe Walnes built a new assertion mechanism on top of what was then JMock 1. The method name was assertThat, and the syntax looked like this:

assertThat(x, is(3));
assertThat(x, is(not(4)));
assertThat(responseString, either(containsString("color")).or(containsString("colour")));
assertThat(myList, hasItem("3"));

More generally:

assertThat([value], [matcher statement]);

Advantages of this assertion syntax include:

• More readable and typeable: this syntax allows you to think in terms of subject, verb, object (assert "x is 3") rathern than assertEquals, which uses verb, object, subject (assert "equals 3 x")

• Combinations: any matcher statement s can be negated (not(s)), combined (either(s).or(t)), mapped to a collection (each(s)), or used in custom combinations (afterFiveSeconds(s))

• Readable failure messages. Compare

  assertTrue(responseString.contains("color") || responseString.contains("colour"));
  // ==> failure message: 
  // java.lang.AssertionError:
  
  
  assertThat(responseString, anyOf(containsString("color"), containsString("colour")));
  // ==> failure message:
  // java.lang.AssertionError: 
  // Expected: (a string containing "color" or a string containing "colour")
  //      got: "Please choose a font"
  

• Custom Matchers. By implementing the Matcher interface yourself, you can get all of the above benefits for your own custom assertions.

• For a more thorough description of these points, see Joe Walnes's original post.:

We have decided to include this API directly in JUnit. It's an extensible and readable syntax, and because it enables new features, like assumptions and theories.

Some notes:

• The old assert methods are never, ever, going away. 
  Developers may continue using the old assertEquals, assertTrue, and so on.

• The second parameter of an assertThat statement is a Matcher. We include the Matchers we want as static imports, like this:

  import static org.hamcrest.CoreMatchers.is;
  

  or:

  import static org.hamcrest.CoreMatchers.*;
  

• Manually importing Matcher methods can be frustrating. [Eclipse 3.3][] includes the ability to define "Favorite" classes to import static methods from, which makes it easier (Search for "Favorites" in the Preferences dialog). We expect that support for static imports will improve in all Java IDEs in the future.

• To allow compatibility with a wide variety of possible matchers, we have decided to include the classes from hamcrest-core, from the Hamcrest project. This is the first time that third-party classes have been included in JUnit.

• To allow developers to maintain full control of the classpath contents, the JUnit distribution also provides an unbundled junit-dep jar, ie without hamcrest-core classes included. This is intended for situations when using other libraries that also depend on hamcrest-core, to avoid classloading conflicts or issues. Developers using junit-dep should ensure a compatible version of hamcrest-core jar (ie 1.1+) is present in the classpath.

• JUnit currently ships with a few matchers, defined in org.hamcrest.CoreMatchers and org.junit.matchers.JUnitMatchers. 
  To use many, many more, consider downloading the full hamcrest package.

• JUnit contains special support for comparing string and array values, giving specific information on how they differ. This is not yet available using the assertThat syntax, but we hope to bring the two assert methods into closer alignment in future releases.

assumeThat

Ideally, the developer writing a test has control of all of the forces that might cause a test to fail. If this isn't immediately possible, making dependencies explicit can often improve a design. 
For example, if a test fails when run in a different locale than the developer intended, it can be fixed by explicitly passing a locale to the domain code.

However, sometimes this is not desirable or possible. 
It's good to be able to run a test against the code as it is currently written, implicit assumptions and all, or to write a test that exposes a known bug. For these situations, JUnit now includes the ability to express "assumptions":

import static org.junit.Assume.*

@Test public void filenameIncludesUsername() {
   assumeThat(File.separatorChar, is('/'));
   assertThat(new User("optimus").configFileName(), is("configfiles/optimus.cfg"));
}

@Test public void correctBehaviorWhenFilenameIsNull() {
   assumeTrue(bugFixed("13356"));  // bugFixed is not included in JUnit
   assertThat(parse(null), is(new NullDocument()));
}

With this beta release, a failed assumption will lead to the test being marked as passing, regardless of what the code below the assumption may assert. In the future, this may change, and a failed assumption may lead to the test being ignored: however, third-party runners do not currently allow this option.

We have included assumeTrue for convenience, but thanks to the inclusion of Hamcrest, we do not need to create assumeEquals, assumeSame, and other analogues to the assert* methods. All of those functionalities are subsumed in assumeThat, with the appropriate matcher.

A failing assumption in a @Before or @BeforeClass method will have the same effect as a failing assumption in each @Test method of the class.

Theories

More flexible and expressive assertions, combined with the ability to state assumptions clearly, lead to a new kind of statement of intent, which we call a "Theory". A test captures the intended behavior in one particular scenario. A theory allows a developer to be as precise as desired about the behavior of the code in possibly infinite numbers of possible scenarios. For example:

@RunWith(Theories.class)
public class UserTest {
  @DataPoint public static String GOOD_USERNAME = "optimus";
  @DataPoint public static String USERNAME_WITH_SLASH = "optimus/prime";

  @Theory public void filenameIncludesUsername(String username) {
    assumeThat(username, not(containsString("/")));
    assertThat(new User(username).configFileName(), containsString(username));
  }
}

This makes it clear that the user's filename should be included in the config file name, only if it doesn't contain a slash. Another test or theory might define what happens when a username does contain a slash.

UserTest will attempt to run filenameIncludesUsername on every compatible DataPoint defined in the class. If any of the assumptions fail, the data point is silently ignored. If all of the assumptions pass, but an assertion fails, the test fails.

The support for Theories has been absorbed from the Popper project, and more complete documentation can be found there.

Defining general statements in this way can jog the developer's memory about other potential data points and tests, also allows automated tools to search for new, unexpected data points that expose bugs.