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 ```python 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!") ```