Thank you! I got confused by the description somehow and didnt think that empty input was an option.

That's not the a & b for test6. Your output will be printed before the error, not after it.
a and b are "5" and "". The empty string causes the exception.

Why not use Console.Writeline to see the input?

Im doing the C# version and all tests pass except for test6:

"System.FormatException : The value could not be parsed." Can't find any issues with the input that would cause this, other tests have larger input.

What is test6 designed to test?

Removed my last comment after checking my code. It seems like I was giving the correct answer.

For test 14 my code does indeed return false, but it still fails. In my mind "}}]]))}])" is about as wrong as it gets so the test case must have an error.

Test14
Expected: True
But was: False
at BraceTests.Test14 () [0x00000] in :0
input: "}}]]))}])"

I dont understand test 14, could you tell me why it should be true?
Edit: Im using C#