JUnit on steroids - JUnit in Action - page 427

@Override
public void evaluate() throws Throwable {
for (Interceptor interceptor:interceptors) {
interceptor.interceptBefore();
}

F
G

H

invoker.evaluate();

for (Interceptor interceptor:interceptors) {
interceptor.interceptAfter();
}
}

I

J

public void addInterceptor(Interceptor interceptor) {
interceptors.add(interceptor);
}
}
As we already discussed, after JU nit 4.5 every test is executed by a block of statements. 1
Here we create our InterceptorStatement by extending the Statement object B ,
and we override the evaluate method F . Our statement holds a statement to invoke
C and a list of Interceptor implementations D that were added to it J . In the con-
structor we initialize the invoker statement E that we're wrapping. The evaluate
method F implements the entire logic of the statement; it iterates over all the inter-
ceptors and invokes their interceptBefore method G . Next we invoke the evaluate
method of the wrapped statement object H and again iterate over all the interceptors,
this time to invoke the interceptAfter method I .
Now that we've prepared the InterceptorStatement object, it's time to move
on and implement the real heart of the custom JU nit runner that we're making. We
do this by extending the BlockJUnit4ClassRunner class, as shown in listing B.3,
which was added in version 4.5 of the JU nit framework to help people create cus-
tom runners.

Listing B.3 Custom JUnit runner— InterceptorRunner

[...]
import org.junit.runners.BlockJUnit4ClassRunner;

B

public class InterceptorRunner extends BlockJUnit4ClassRunner {

C

@Retention( RetentionPolicy.RUNTIME )
@Target( ElementType.TYPE )
public @interface InterceptorClasses {

D

public Class<?>[] value();

}

public InterceptorRunner(Class<?> clazz) throws InitializationError {
super ( clazz );
} E

1

For more on this topic you can read an article by Kent Beck here: http://threeriversinstitute.org/
TwoMoreImplementationPatterns.htm.