In the code below, you need to write unit tests to evaluate a function named add_three_digits.

• add_three_digits(digits: str) -> int: Consumes a string of three digits (e.g., "123"), converts each digit to an integer, and produces their sum. If any characters are not digits, or if there are not three digits, then the integer 0 should be returned instead.

You should not implement the add_three_digits function yourself!

Instead, your job is to write a collection of unit tests that:

• will all pass when provided a genuine implementation of the function (“Valid Tests”)
• at least one will fail when provided an impostor implementation of the function (“Thorough Tests”)

add_three_digits is only available when you submit. In the sandbox (To sandbox, then Run), running your code only lists your tests: it can’t tell you whether they pass.