The question setter or Tester provide input testcases, so I dont think testcases contains any type of bugs.
see this
https://discuss.codechef.com/questions/126761/wrong-test-input-in-stmincut?page=1#126931
it is possible to have bug in input test caes.
I totally aggred with You!
Exactly what I said, that most of test cases are maximal. But I think editorials can help for smaller cases wherever applicable 
Doesnt encourage thinking about edge cases.Also, what if lot of edge cases there?
Doesnt address main things like “Most of TC are huge and hence of no use.” Also, instead of buting using karma, the present system of asking n awarding karma is better and more sustainable
Yeah, but it helps in the following cases:
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- deciding whether solution would have passed through just optimizations or it was an edge case. It has mostly happens when I submit using python (like passing 19 out of 20 test cases).
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- many of the codechef questions have a testcase file comprised of various test cases(which individually may not be very large to deal with). We can just find the failing case using diff of expected answer and my answer.
Buying using karma may promote more engagement with the discuss community. Also this will help in the case where beginners won’t be able to harm themselves by just looking at the test cases. There is a +ve covariance between ratings and karma to some extent.