The normal expected functionality with the enter a comment form in the sandbox app is broken.
Test 1: Post Functionality Error
Login with username=alice and password=monkey1. What happens if you create a comment? Does it work in the same way that it did before you changed the code? You can reset the sandbox to find out.
Test 2: Post Functionality Is Broken Error
Login with username=alice and password=monkey1. What happens if you create a second comment? Does it work in the same way that it did before you changed the code? You can reset the sandbox to find out.
Test 3: Post Functionality Is Broken Error
What if you login with username=bob and password=password. What happens if you create a new comment? Does it work in the same way that it did before you changed the code? You can reset the sandbox to find out.