testing - Writing Java tests with data providers

Question

I'm currently doing my first Java project and like to fully TDD it. I'm using JUnit for writing the tests. Apparently JUnit does not provide support for data providers, which makes it rather annoying to test the same method with 20 different versions of an argument. What is the most popular/standard testing tool for Java that does support data providers? I came across TestNG, but have no idea how popular that one is, or how it compares to alternatives.

If there is a way to get this behaviour is a nice way using JUnit, then that might also work.

Answer 1

Coworkers of mine at our company wrote a freely available DataProvider in TestNG style for JUnit which you can find on github (https://github.com/TNG/junit-dataprovider).

We use it in very large projects and it works just fine for us. It has some advantages over JUnit's Parameterized as it will reduce the overhead of separate classes and you can execute single tests as well.

An example looks something like this

@DataProvider
public static Object[][] provideStringAndExpectedLength() {
    return new Object[][] {
        { "Hello World", 11 },
        { "Foo", 3 }
    };
}

@Test
@UseDataProvider( "provideStringAndExpectedLength" )
public void testCalculateLength( String input, int expectedLength ) {
    assertThat( calculateLength( input ) ).isEqualTo( expectedLength );
}

Edit: Since v1.7, it also supports other ways to provide data (strings, lists) and can inline the provider so that a separate method is not necessarily needed.

A full, working example can be found on the manual page on github. It also has a few more features, like collecting the providers in utility classes and accessing them from other classes etc. The manual page is very detailed, I'm sure you'll find any questions answered there.