JUnit on steroids - JUnit in Action - page 420

in the way things are done. Remember that you can include the @BeforeClass and
@AfterClass annotated methods in the suite. This wasn't possible with the 3.x versions
of JU nit.

A.4.3 Parameterized tests

As you saw, the @RunWith annotation lets you define a test runner to use. The Suite
test runner that we already presented lets you run your test cases in a suite.
Another test runner that's bundled with the JU nit distribution is the Parameterized
test runner. This test runner lets you run the same tests with different input test
data. We know that an example is worth several pages of explanation, so listing A.10
shows the example.

Listing A.10 Parameterized test runner in action

@RunWith(value=Parameterized. class )
public class SquareRootTest {

B

private int expected;
private int actual;

C

@Parameters
public static Collection data() {
return Arrays.asList( new Object[][] {
{ 1, 1 },
{ 2, 4 },
{ 3, 9 },
{ 4, 16 },
{ 5, 25 },
});
}

D

public SquareRootTest( int expected, int actual) {
this. expected = expected;
this .actual = actual;
}

E

@Test
public void squareRoot() {
Calculator calculator = new Calculator();
assertEquals(expected, calculator.squareRoot(actual));
}
}
Imagine that we have a squareRoot method in our Calculator class that we want to
test. This listing demonstrates how to test this method with different input test data. We
start by declaring the use of the Parameterized test runner at B . Then, at C , we
define the static data() method that we annotate with @Parameters , denoting that this
method returns the actual test data for our test. This test data is made from a
java.util.List , and each element of the List is a two-dimensional array, the ele-
ments of which will be used to make a new instance of the SquareRootTest . At D we fill
in the test data and return it. At E we start the test method, and inside it we instantiate

F