Java – how do I use a JUnit parameterized runner with a varargs constructor?

I wrote a model example to illustrate this without divulging any confidential information This is a "virtual" example that does nothing, but the problem occurs in the test initializer

@RunWith(Parameterized.class)
public class ExampleParamTest
{
 int ordinal;
 List<String> strings;

 public ExampleParamTest(int ordinal,String... strings)
 {
  this.ordinal = ordinal;
  if (strings.length == 0)
  {
   this.strings = null;
  }
  else
  {
   this.strings = Arrays.asList(strings);
  }
 }

 @Parameters
 public static Collection<Object[]> data() {
  return Arrays.asList(new Object[][] {
    {0,"hello","goodbye"},{1,"farewell"}
  });
 }

 @Test
 public void dotest() {
  Assert.assertTrue(true);
 }
}

Basically, I have a test constructor that accepts multiple parameters of a local list variable, and I want to populate it with an array initializer The test method will handle local list variables correctly – I have removed this logic to simplify the test

When I wrote this article, my ide had no complaints about syntax and test class construction, and there were no compilation errors But when I run it, I get:

doTest[0]:
java.lang.IllegalArgumentException: wrong number of arguments
  at java.lang.reflect.Constructor.newInstance(UnkNown Source)
doTest[1]:
java.lang.IllegalArgumentException: argument type mismatch
  at java.lang.reflect.Constructor.newInstance(UnkNown Source)

What's wrong here and how can I use this model correctly?

Solution

I can't test it now, but I think if you call a method or constructor with variable parameters, you must use an array instead of a list of variable values to call it

If I'm right, then this should work:

@Parameters
 public static Collection<Object[]> data() {
  return Arrays.asList(new Object[][] {
    {0,new String[]{"hello","goodbye"}},new String[]{"farewell"}}
  });
 }

Some explanation

At the source level, we can write

test = ExampleParamTest(0,"one","two");

The compiler converts it to a string array JUnit uses reflection and call APIs. From this point of view, constructor signatures are

public ExampleParamTest(int i,String[] strings);

Therefore, to call the constructor - which is what JUnit does internally - you must pass an integer and a string array