Write a code snippet demonstrating how to debug a failed test case in a testing script.

Sure, here is a simple example of how you might debug a failed test case in Python using the built-in unittest module and pdb for debugging:

import unittest
import pdb

class TestMyFunction(unittest.TestCase):
    def test_add(self):
        result = add(10, 5)
        self.assertEqual(result, 15)

def add(a, b):
    pdb.set_trace()  # Set a breakpoint here
    return a + b

if __name__ == '__main__':
    unittest.main()

In this example, we have a simple test case for a function add that adds two numbers. If the test case fails, the Python debugger pdb will stop at the line where we called pdb.set_trace().

You can then inspect the current state of the program, print variable values, step through the code one line at a time, etc. This can help you understand why the test case is failing.

To continue execution after the debugger has stopped, you can use the continue command. To step through the code one line at a time, you can use the next command. To print the value of a variable, you can use the print command followed by the variable name.

Remember to remove or comment out the pdb.set_trace() line once you're done debugging.