JUnit on steroids - JUnit in Action - page 433

public void describeTo( Description description ) {
description.appendText("a string that is not null and not empty");
}

D

@Factory
public static <T> Matcher<String> isNotNullOrEmpty() {
return new IsNotNullOrEmpty();
}

E

@Factory
public static <T> Matcher<String> notNullOrEmpty() {
return new IsNotNullOrEmpty();
}
}
Basically, if we want to create a custom matcher, we need to extend one of the two
classes BaseMatcher<T> or TypeSafeMatcher<T> . In this listing, we extend the first
one B . Next, we override the matches method C , and we implement our logic on
what occasion the matcher will match the conditions; our condition is matched suc-
cessfully if the string parameter to which it is applied is not null and is different from
an empty string.
Here comes the difference between BaseMatcher<T> and TypeSafeMatcher<T> . As
you'll see later, if you extend TypeSafeMatcher<T> , then you'll have to override
another method with the signature

protected boolean matchesSafely(T item);
This means that the method that has to implement our logic can never accept a null
object. It will always accept a parameter of type T , which has already been checked for
null value and can never be null . We want to implement this check, however, so we
stick with the BaseMatcher<T> class .
In D we append a description for the matcher. This description is used in our test
cases in case the matcher can't match the condition. In E we provide two factory
methods (denoted by the @Factory annotation). We call these methods from our test
cases to create an instance of our matcher. We provide two methods, only for readabil-
ity purposes; sometimes it will be more readable to call one of them and sometimes
the other.
Listing B.9 shows the corresponding test class that uses our test methods.

Listing B.9 Test class to demonstrate the IsNotNullOrEmpty matcher

[...]

import static com.manning.junitbook.appD.custom.matchers
.IsNotNullOrEmpty.isNotNullOrEmpty;
import static com.manning.junitbook.appD.custom.matchers
.IsNotNullOrEmpty.notNullOrEmpty;

B

public class TestStringIsNullUsingMatcher {

C

@Test(expected=java.lang.AssertionError. class )
public void testIsNotNullOrEmptyButIsNull() {