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https://github.com/greghaskins/parametric-junit-runner

A JUnit test runner that makes it easy for developers to write parameterized test cases
https://github.com/greghaskins/parametric-junit-runner

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A JUnit test runner that makes it easy for developers to write parameterized test cases

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Parametric JUnit Runner

=======================



A JUnit test runner that makes it easy for developers to write parameterized test cases. I created `Parametric` as an exercise to devise a better parameterized testing API than the one used with JUnit's `Parameterized` runner. When teaching TDD, I find the `Parameterized` runner is slightly too difficult to grok for beginners, to the point where I would not recommend using it even in situations where it might be useful.



Example

-------



A contrived example would be testing an `Adder` object whose responsibility is to compute the sum of two integers. Rather than creating many similar test cases with expected results, an enterprising developer might parameterize the tests:



```java

@RunWith(Parametric.class)

public class AdderTest {



	private final int left;

	private final int right;

	private final long expectedSum;



	public AdderTest(final int left, final int right, final long expectedSum) {

		this.left = left;

		this.right = right;

		this.expectedSum = expectedSum;

	}



	@TestCases

	public static Iterable testCases() {

		final ArrayList cases = new ArrayList();

		cases.add(new AdderTest(1, 2, 3));

		cases.add(new AdderTest(8, 46, 54));

		cases.add(new AdderTest(42, 0, 42));

		cases.add(new AdderTest(-3, 3, 0));

		cases.add(new AdderTest(44728, 2346, 47074));

		cases.add(new AdderTest(2147483647, 3, 2147483650L));

		return cases;

	}



	@Override

	public String toString() {

		return MessageFormat.format("{0} and {1} make {2}", 

									this.left, this.right, this.expectedSum);

	}



	@Test

	public void additionIsPerformedCorrectlyLeftToRight() {

		final Adder adder = new Adder();

		final long sum = adder.add(this.left, this.right);

		assertThat(sum, is(equalTo(this.expectedSum)));

	}



	@Test

	public void additionIsCommutativeRightToLeft() {

		final Adder adder = new Adder();

		final long sum = adder.add(this.right, this.left);

		assertThat(sum, is(equalTo(this.expectedSum)));

	}

}

```



Comparison to `Parameterized`

-----------------------------



`Parametric` provides very similar functionality to JUnit's `Parameterized` runner, however it preserves compile-time type checking and readability by not calling constructors reflectively. The above example could be written using the `Parameterized` runner as follows:



```java

	@Parameters(name = "{0} and {1} make {2}")

	public static Iterable getParameters() {

		final ArrayList cases = new ArrayList();

		cases.add(new Object[] { 1, 2, 3 });

		cases.add(new Object[] { 8, 46, 54 });

		cases.add(new Object[] { 42, 0, 42 });

		cases.add(new Object[] { -3, 3, 0 });

		cases.add(new Object[] { 44728, 2346, 47074 });

		cases.add(new Object[] { 2147483647, 3, 2147483650L });

		return cases;

	}

```



Unless you are accustomed to reading code that reflectively provides method parameters, the above can be somewhat confusing at first. Additionally, the `name` attribute of the `@Parameters` annotation is convenient, but not obvious to many developers.



To-Do

-----



- Compile-time, inline warnings and errors for invalid `Parametric` test classes

- Fix `@BeforeClass` and `@AfterClass` so they are not executed for each test case

- A more explicit way to provide the test case name than overriding `toString()`