How to write and apply JUnit Rules.

Applying Rules

public class MyTest {
    @Rule
    public MethodRule screenshot = new ScreenshotOnFailureRule();

    @Test
    public void myTest() { ... }

    ...
}

Writing Rules with Decisions

public class ScreenshotOnFailureRule implements MethodRule {
    @Override
    public Statement apply(Statement base, FrameworkMethod method, Object target) {
        if(allowsScreenshot(method)) {
            String className = method.getMethod().getDeclaringClass().getSimpleName();
            String methodName = method.getName();
            return new ScreenshotOnFailureStatement(base, className, methodName);
        }
        else {
            return base;
        }
    }

    private boolean allowsScreenshot(FrameworkMethod method) {
        return method.getAnnotation(NoScreenshot.class) == null;
    }
}

Writing Simple Rules

public class ScreenshotOnFailureRule implements MethodRule {
    @Override
    public Statement apply(Statement base, FrameworkMethod method, Object target) {
        String className = method.getMethod().getDeclaringClass().getSimpleName();
        String methodName = method.getName();
        return new ScreenshotOnFailureStatement(base, className, methodName);
    }
}

Writing Statements

public class ScreenshotOnFailureStatement extends Statement {
    private final Statement base;
    private final String className;
    private final String methodName;

    public ScreenshotOnFailureStatement(Statement base, String className, String methodName) {
        this.base = base;
        this.className = className;
        this.methodName = methodName;
    }

    @Override
    public void evaluate() throws Throwable {
        try {
            base.evaluate();
        }
        catch(Throwable e) {
            MyScreenshooter.takeScreenshot(className, methodName);
            throw e;
        }
    }
}

Note: These examples are for JUnit 4.8.2. In JUnit 4.9, MethodRule will be replaced by TestRule, which has a slightly different interface.