Regex Tester

Usage

When the user asks you to create, validate, or debug a regular expression:

1. Understand the requirement — clarify what the pattern should match and what it should reject.
2. Consult the cheatsheet — review references/regex-cheatsheet.md for syntax reminders if needed.
3. Write and execute test code — use the execute_code tool to run Python code that:
   • Compiles the regex with re.compile()
   • Tests it against a set of positive examples (should match) and negative examples (should not match)
   • Extracts and displays any capturing groups
   • Reports pass/fail for each test case
4. Iterate — if any test fails, refine the pattern and re-run until all cases pass.
5. Present the result — give the user the final pattern, explain what each part does, and show the test results.

Example Test Script

import re

pattern = re.compile(r'^[\w.+-]+@[\w-]+\.[\w.-]+$')

positives = ["user@example.com", "first.last+tag@sub.domain.org"]
negatives = ["@missing.com", "no-at-sign", "spaces in@address.com"]

for s in positives:
    assert pattern.match(s), f"FAIL: expected match for '{s}'"
for s in negatives:
    assert not pattern.match(s), f"FAIL: expected no match for '{s}'"

print("All tests passed!")