I would like to test that
My answer was: ich würde gerne das testen. However, Duolingo said it was wrong. The correct answer was: Das würde ich ja gerne mal testen. What? (1) I think my answer is correct. (2) What is Duolingo doing throwing in those modal particles ("ja" and "mal"). As another possible correct answer, I can understand: Das würde ich gerne testen. But the answer given seems way to idiosyncratic.
Clarification would be appreciated.
This really happens a lot that after answering wrong, Duolingo shows you a correct answer that is very different from the way you tried to answer, rather than just "correcting" your sentence. Exactly like in your example where just the word order was wrong but it showed you a very fancy way to say the same thing. It is quite annoying but you'll get used to it eventually. Take it as a chance to see alternative ways of saying things.
you said "ich würde gerne das testen". the probleme with this sentence is you put the "das" in the wrong place. it must be "ich würde das gerne testen".
so the "das" has to be placed before the "gerne".
the answer they gave you is correct as well but more complicated. since i have no reason to do a german course i do not know if they would accept my sentence or if they really need to have it as " das würde ich ja gerne mal testen".