What happened with the practice test in the lingot store??
One of the nicest stuff of Duolingo was the test with grade as I could see my advance from one to another but now I only see the Timed Practice, without it the lingots became useless for me :/ what happened Duolingo??
Progress quiz (we would rather focus efforts on creating other, more popular shop items)
Duolingo Help Center Updates News "Duolingo's New Website"
Last updated: June 15, 2017
They re-wrote the website; I think some of the goals were to make it faster and more easily extensible.
This was one of the features of the old website which they haven't yet re-created on the new one.
So they haven't explicitly removed it; just haven't re-done it in the new version.
As Pentaan wrote, it's on their list of things they know are not available in the new one and which may come "back" at some point. (But we don't know when or if.)