# Running Parameterized JUnit Tests

The `Parameterized`

test runner allows you to run a test many times with different sets of parameters. To run a test class with the `Parameterized`

test runner, you must meet the following requirements.

- The test class must carry the
`@RunWith`

annotation with the`Parameterized`

class as its argument. - The test class must declare instance variables used in the tests.
- Provide a method annotated with
`@Parameters`

. The signature of this method must be`@Parameters public static java.util.Collection`

, without parameters. The`Collection`

elements must be arrays of identical length. This array length must match the number of arguments of the only public constructor. - The test class must have a constructor matching the elements in the array.

```
package com.memorynotfound.test;
import com.memorynotfound.Math;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameters;
import java.util.Arrays;
import java.util.Collection;
import static org.junit.Assert.assertEquals;
@RunWith(Parameterized.class) // => #1
public class ParametrizedTest {
private final int input; // => #2
private final int expected;
public ParametrizedTest(int input, int expected) { // => #4
this.input = input;
this.expected = expected;
}
@Parameters // => #3
public static Collection
``` data(){
return Arrays.asList(new Integer[][] {
{0,1},{1,1},{2,2},{3,6},{4,24},{5,120}});
}
@Test
public void calculatorAddTest(){
System.out.println("factorial of: " + input + " should be: " + expected);
assertEquals(expected, Math.fact(input));
}
}

```
package com.memorynotfound;
public class Math {
public static int fact(int n) {
int result;
if (n==0 || n==1)
return 1;
result = fact(n-1) * n;
return result;
}
}
```

Generated output

```
factorial of: 0 should be: 1
factorial of: 1 should be: 1
factorial of: 2 should be: 2
factorial of: 3 should be: 6
factorial of: 4 should be: 24
factorial of: 5 should be: 120
```