I'd honestly say that it's better if you can't view test cases. In most if not all contests, tests cases are hidden, so it makes sense for them to be hidden during practice. Plus, it improves your debugging skills :)

But, even if it's ideal or not, I'm pretty sure that codeforces doesn't have a feature of viewing all the test cases...

You can atleast get the input on which you get wrong answer using this method:

See this solution. In the 2nd testcase, on test 324, the code gives WA according to jury.

Now see this modified code. The passed testcases can be put as t==... separated by || (see code), else the input for the test number can be displayed.