JUnitExt Prerequisite as JUnit 4.7 Rule

The JUnit 4 Extensions project provides a annotation for specify precondition for a test. For example you have a database integration test, it makes no sense to run this test when the database is down. Therefor you can use the JUnit 4 Extension annotation @Prerequisite. But the disadvantage is, you must use a JUnit 4 Extension specific JUnit test runner @RunWith(AnnotationRunner.class). The Problem with the runner is when you must use a other runner for example the spring DI test runner in the test the approach did not work well.

But a feature like the @Prerequisite annotation of JUnit 4 Extensions project is very nice to have. In JUnit 4.7 there for the JUnit rules comes in mind, here is a small code example how a rule solution for the @Prerequisite annotation can look like.


Here the test with the @Prerequisite annotation and without specific test runner:

public class DatabaseTest {

 @Rule
 public PrerequisiteRule rule = new PrerequisiteRule(); 
 
 @Test
 @Prerequisite(requires="databaseIsAvailable")
 public void testFindAllUsers() throws Exception {
  // Database test stuff here
 }
 
 @Test
 public void testGetDataSource() throws Exception {
  // No Database test stuff here
 }
 
 public boolean databaseIsAvailable(){
  return false;
 }
  
}

The test result will be:

This test without errors can look like this one:

public class DatabaseTest {

 @Rule
 public PrerequisiteRule rule = new PrerequisiteRule(); 
 
 @Test
 @Prerequisite(requires="databaseIsAvailable")
 public void testFindAllUsers() throws Exception {
  // Database test stuff here
 }
 
 @Test
 public void testGetDataSource() throws Exception {
  // No Database test stuff here
 }
 
 public boolean databaseIsAvailable(){
  return true;
 }
 
 
}

And here a very basic rule implementation for the test:

public class PrerequisiteRule implements MethodRule{

 public Statement apply(final Statement base, final FrameworkMethod method, final Object target) {
  return new Statement() {
   @Override
   public void evaluate() throws Throwable {
    Prerequisite annotation = method.getMethod().getAnnotation(Prerequisite.class);
    if(annotation != null){
     String requiresMethodname = annotation.requires();
     Method requiresMethod = target.getClass().getMethod(requiresMethodname);
     Boolean result = (Boolean) requiresMethod.invoke(target);
     if(!result.equals(true)){
      fail("Test requires "+requiresMethodname);
     }
    }
    base.evaluate();
   }
  };
 }

}

Ok the implementation of the rule is very basic there is no good error handling for example ...

Feel free for comments ...

Links:
- http://junitext.sourceforge.net/
- http://www.junit.org/