Rule (JUnit API)
Date: 2016-08-24

org.junit

## Annotation Type Rule

-     @Retention(value=RUNTIME)
       @Target(value={FIELD,METHOD})
      public @interface Rule

  Annotates fields that reference rules or methods that return a rule. A field must be public, not static, and a subtype of `TestRule` (preferred) or `MethodRule`. A method must be public, not static, and must return a subtype of `TestRule` (preferred) or `MethodRule`.

  The `Statement` passed to the `TestRule` will run any `Before` methods, then the `Test` method, and finally any `After` methods, throwing an exception if any of these fail. If there are multiple annotated `Rule`s on a class, they will be applied in order of fields first, then methods. However, if there are mutliple fields (or methods) they will be applied in an order that depends on your JVM's implementation of the reflection API, which is undefined, in general. Rules defined by fields will always be applied before Rules defined by methods.

  For example, here is a test class that creates a temporary folder before each test method, and deletes it after each:

       public static class HasTempFolder {
           @Rule
           public TemporaryFolder folder= new TemporaryFolder();

           @Test
           public void testUsingTempFolder() throws IOException {
               File createdFile= folder.newFile("myfile.txt");
               File createdFolder= folder.newFolder("subfolder");
               // ...
           }
       }

  And the same using a method.

       public static class HasTempFolder {
           private TemporaryFolder folder= new TemporaryFolder();

           @Rule
           public TemporaryFolder getFolder() {
               return folder;
           }

           @Test
           public void testUsingTempFolder() throws IOException {
               File createdFile= folder.newFile("myfile.txt");
               File createdFolder= folder.newFolder("subfolder");
               // ...
           }
       }

  For more information and more examples, see `TestRule`.
  Since:
    4.7