Testing, testing testing. Any more (sometimes even less) self-respecting freelance, writing site (of any kind) will have a test of some shape or form for aspiring writers trying to join.
As a freelance writer, there are two ways you can approach this through song: the more famous way, with The Beatles “I’m So Tired” or the less famous from the Seventies American female duo The Roches, “Keep On Doing”.
Not only is the first song solution more famous, it is also very tempting - you’ve done so much, studied so much, put in so much effort, and you are still being tested, reminding you of all those fourth grade spelling tests… And not only that, they keep on asking you for sample work “done for a better known outlet”, as if you would be there, being tested, if you are already have ‘ample’ published work for a “known outlet”.
But, although the second song solution is neither so famous nor attractive, it is probably the way to go. First of all, most of the sites or organisations requesting that you be tested want to be sure they are getting writers that fit their criteria. Even though you might not like it, or you do not see it fit, it is a certain criteria and will probably offer you a better chance of getting respectable jobs. If you get in, of course.
One more thing - you are getting to write and/or research. And this time not only are you practicing, your writing has a definite purpose. As an extra incentive, some outlets pay you for doing the test. You don’t mind getting paid, do you?
Submitting sample work should not be the thing to worry you. Even if the work you have published might not be for the most known site or organisation around, if it is good, it will be taken into serious consideration.
What should you take care of is that resume or cover letter (usually both) that you will have to submit. Stay away, but always from a generic letter, one that is not tailored specifically for the organisation that you are applying to. Of course they don’t know what letter you submitted to another outlet. But, they have seen so many of those that they will instantly know whether it is one you already submitted somewhere else or you whether you took in their specifics.
If you don’t respect that, you might be rejected, no matter how ell you do their test. And then, just “Keep on Doing It”. Consider the alternatives.