I face the same problem "We can't find the last successful test run that invokes the testIterableForLoop method. Run the test again and check the test run results for more details.".

Hi Community, 

The below test class helped me pass the challenge. Run this class from  

 * @description Test class for MyIterable

 * Tests the custom Iterable implementation for String lists

 */

@isTest

private class MyIterableTest {

    /**

     * @description Test constructor and iterator with a valid list of strings

     */

    @isTest

    static void testIterableForLoop() {

        // Arrange

        List<String> strings = new List<String>{'Hello','World'};

        Test.startTest();

        // Act

        MyIterable myIterable = new MyIterable(strings );

        Iterator<String> iterator = myIterable.iterator();

        List<String> iteratedStrings = new List<String>();

        while (iterator.hasNext()) {

            iteratedStrings.add(iterator.next());

        }

        Test.stopTest();

        System.debug(iteratedStrings[0]);

        System.debug(iteratedStrings[1]);

        // Assert

        Assert.areEqual(2, iteratedStrings.size(), 'Should iterate over all 2 strings');

        Assert.areEqual('Hello', iteratedStrings[0], 'First element should be Hello');

        Assert.areEqual('World', iteratedStrings[1], 'Second element should be World');

    }

}