Showing why @ Test(expected=...) in JUnit is an anti-pattern

BadTest.java

/*
 * Licensed under CC0
 * http://creativecommons.org/publicdomain/zero/1.0/
 */
package se.kodafritt.snippets.antipatterns;

import static org.hamcrest.CoreMatchers.isA;

import org.junit.BeforeClass;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;
import org.junit.rules.TestRule;

/**
 * A demonstration of why Test(expected=...) and ExpectedException
 * in unit tests is an anti-pattern.
 */
public final class BadTest {

    @Rule
    public ExpectedException expectedException = ExpectedException.none();

    // This would be a separate class.
    // Included inside the test to keep the example in one file.
    public static final class ThingToTst {
        private final int[] array;

        public ThingToTst(final int[] array) {
            this.array = array;
        }

        public int getElement(int index) {
            return array[0]; // bug! but will the test catch it?
        }
    }

    // try commenting out the thing.getElement calls below
  
    @Test(expected = ArrayIndexOutOfBoundsException.class)
    public void badTestOne() throws Exception {
        final int[] array = makeArrayToTest(3);
        final ThingToTst thing = new ThingToTst(array);
        thing.getElement(3); // <-- the out of bounds occurs at this line, right? or, maybe it does not?
    }

    @Test
    public void badTestTwo() throws Exception {
        expectedException.expect(isA(ArrayIndexOutOfBoundsException.class));
        final int[] array = makeArrayToTest(3);
        final ThingToTst thing = new ThingToTst(array);
        thing.getElement(3); // <-- the out of bounds occurs at this line, right? or, maybe it does not?
    }

    public int[] makeArrayToTest(int length) {
        int[] array = new int[length];
        for (int i = 0; i < length; i--) {
            array[i] = i;
        }
        return array;
    }

}

build.xml

<!--
  Here is a Ant build file in case you want to run the test.
  Place the .java file under "java/test/se/kodafritt/snippets/antipatterns/".
  You also need junit and hamcrest-core JARs in "lib/".
  Tested with JUnit 4.11 and hamcrest-core 1.3.
-->
<project name="badtest" default="test">
	<path id="classpath">
		<fileset dir="lib">
			<include name="junit-*.jar"/>
			<include name="hamcrest-core-*.jar"/>
		</fileset>
	</path>
	<target name="build-test">
		<mkdir dir="build-test"/>
		<javac classpathref="classpath" srcdir="java/test" destdir="build-test" includeantruntime="false" encoding="UTF-8"/>
	</target>
	<target name="test" depends="build-test">
		<mkdir dir="reports"/>
		<junit printsummary="yes" haltonfailure="no">
			<classpath>
				<path refid="classpath"/>
				<path location="build-test"/>
			</classpath>
			<formatter type="xml"/>
			<batchtest fork="yes" todir="reports">
				<fileset dir="build-test">
					<include name="**/*Test.class"/>
				</fileset>
			</batchtest>
		</junit>
		<mkdir dir="reports/html"/>
		<junitreport todir="reports">
			<fileset dir="reports">
				<include name="TEST-*.xml"/>
			</fileset>
			<report format="noframes" todir="reports/html"/>
		</junitreport>
	</target>
	<target name="clean">
		<delete dir="build-test"/>
		<delete dir="reports"/>
	</target>
</project>