Write a Python CLI script called word_count.py that:
- Accepts a filename argument using argparse
- Reads the file and counts: total words, unique words, top 5 most common words
- Uses pathlib.Path for file access, collections.Counter for word counting
- Uses type hints throughout
- Handles FileNotFoundError gracefully with a helpful error message
- Prints results in a clean formatted table using f-strings

Include pytest unit tests that test the counting logic with a tmp_path fixture.
