You can't

What's the use, are you going to debug such a long test case?

It's very difficult to debug your solution even if you get hold of the large testcase.

But if the problem has smaller testcases after the failing one, you can use CF Debug to (possibly) find a counter example to your logic.

https://codeforces.com/blog/entry/4065

This post shows the answer how, i won't summarize here.

"necroposting" to avoid the same -ve affect on others as this post in its current state ("not possible") discouraged me, and it was shown top on web search.

No, it's not possible -_-.

It's not possible.

There are some sites where you can compare your code with the solution. But you need a subscription over $100 per year.

Not revealing test cases can be annoying but it will actually improve your debugging skills so don't be mad about that