Writing a parameterized test fails with: There was an error retrieving the parameters for the testcase: cause invalid value for parameterized field

I have a few unit tests that require very large strings for the test data. I do not want to declare the HTML string in the test itself as this can obscure that actual test. Rather, I would like to load these strings from an external resource for each test.

Though I am not running the same test with different sets of data, parameterized tests looks to be a viable solution; however, I am having difficulty getting the following example to work.

Note: This code is based on the TestNG example.

package flexUnitTests
{
    import helpers.HTMLDataHelper;

    import org.flexunit.runners.Parameterized;
    import org.hamcrest.assertThat;
    import org.hamcrest.text.containsString;

    [RunWith("org.flexunit.runners.Parameterized")]
    public class SimpleTestCase
    {
        private var parameterized:Parameterized;

        public static var dataLoader:HTMLDataHelper = new HTMLDataHelper("data/layer.html");

        [DataPoint(loader="dataLoader")]
        public static var htmlContent:String;

        [Test(dataprovider="htmlContent", description="Tests something.")]
        public function mustPassThisSimpleTest(htmlContentParam:String):void
        {
            assertThat(htmlContentParam, containsString("head"));
        }
    }
}

When I run this test I receive the following error message:

Error: There was an error retrieving the parameters for the testcase: cause invalid value for parameterized field htmlContent: null

Any thoughts as to what might be the solution to this problem might be?

One solution I found was to run the tests in the class with the Theories runner as shown below.

package flexUnitTests
{
    import helpers.HTMLDataHelper;

    import org.flexunit.experimental.theories.Theories;
    import org.flexunit.runners.Parameterized;
    import org.hamcrest.assertThat;
    import org.hamcrest.object.equalTo;
    import org.hamcrest.text.containsString;

    [RunWith("org.flexunit.experimental.theories.Theories")]
    public class SimpleTestCase
    {
        public static var dataLoader:HTMLDataHelper = new HTMLDataHelper("data/layer.html");

        [DataPoint(loader="dataLoader")]
        public static var htmlContent:String;

        [Test(dataprovider="htmlContent", description="Tests something.")]
        public function mustPassThisSimpleTest(htmlContentParam:String):void
        {
            assertThat(htmlContentParam, containsString("head"));
        }
    }
}

However the side effect is that all of your tests within the test class will display cryptic error messages when the tests fail. For example,

Error: mustWorkWithRegularTests

instead of the much more useful

Error: Expected: a string containing "head"
but: was "this is some text"

Though this does "solve" the problem I was having, IMHO the trade off in message clarity is not worth being able to load data from external sources.