Support debugging of test cases

[jorsanpe]

Sometimes it's useful to run the debugger in order to find a problem with a test case. The problem right now is that, as the describe statement is a macro, the C++ debugger seems not capable of doing steps in the test cases themselves. It seems that the problem is related to GDB not supporting debugging of lambda functions. I think in order to fix this describe should not expand to a lambda function, same as the it statements.

[cegonse]

This has top priority!