Rules are used to enhance the behaviour of each test method in a generic way. Junit rule intercept the test method and allows us to do something before a test method starts execution and after a test method has been executed.
For example, Using @Timeout rule we can set the timeout for all the tests.
public class TestApp {
@Rule
public Timeout globalTimeout = new Timeout(20, TimeUnit.MILLISECONDS);
......
......
}
@TemporaryFolder rule is used to create temporary folders, files. Every time the test method is executed, a temporary folder is created and it gets deleted after the execution of the method.
public class TempFolderTest {
@Rule
public TemporaryFolder tempFolder= new TemporaryFolder();
@Test
public void testTempFolder() throws IOException {
File folder = tempFolder.newFolder("demos");
File file = tempFolder.newFile("Hello.txt");
assertEquals(folder.getName(), "demos");
assertEquals(file.getName(), "Hello.txt");
}
}
You can see examples of some in-built rules provided by junit at this link.