feat(5.3): Add Update Checker — compare installed vs latest versions

Add scripts/update_checker.py — dependency health monitor that checks
installed Python packages against PyPI latest, classifies updates by
semver (major/minor/patch), flags breaking changes, and outputs a
human-readable or JSON report.

Acceptance criteria:
  ✓ Compares installed vs latest via pip list + PyPI JSON API
  ✓ Reports major/minor/patch updates with severity (high/medium/low)
  ✓ Flags breaking changes (major version jumps)
  ✓ Output: formatted text report or --json machine report

Also adds comprehensive test suite (11 tests, all passing).

Refs: #109

tests/test_update_checker.py

@@ -0,0 +1,212 @@
+#!/usr/bin/env python3
+"""
+Tests for update_checker.py — 5.3: Update Checker
+
+Acceptance criteria verified:
+  ✓ Compares installed vs latest
+  ✓ Reports major/minor/patch updates  
+  ✓ Flags breaking changes (major)
+  ✓ Output: update report
+"""
+
+import json
+import os
+import subprocess
+import sys
+import tempfile
+from datetime import datetime
+from pathlib import Path
+from unittest.mock import patch, MagicMock
+
+# Add scripts dir to path
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "scripts"))
+
+import update_checker as uc
+
+
+def test_parse_version():
+    assert uc.parse_version("1.2.3") == (1, 2, 3)
+    assert uc.parse_version("2.0.0") == (2, 0, 0)
+    assert uc.parse_version("0.9.0") == (0, 9, 0)
+    assert uc.parse_version("1.2") == (1, 2, 0)
+    assert uc.parse_version("1") == (1, 0, 0)
+    assert uc.parse_version("invalid") == (0, 0, 0)
+    print("PASS: parse_version")
+
+
+def test_classify_update_patch():
+    result = uc.classify_update("1.2.3", "1.2.4")
+    assert result is not None
+    assert result['update_type'] == 'patch'
+    assert result['breaking_change'] is False
+    assert result['severity'] == 'low'
+    print("PASS: classify_update_patch")
+
+
+def test_classify_update_minor():
+    result = uc.classify_update("1.2.3", "1.3.0")
+    assert result is not None
+    assert result['update_type'] == 'minor'
+    assert result['breaking_change'] is False
+    assert result['severity'] == 'medium'
+    print("PASS: classify_update_minor")
+
+
+def test_classify_update_major():
+    result = uc.classify_update("1.2.3", "2.0.0")
+    assert result is not None
+    assert result['update_type'] == 'major'
+    assert result['breaking_change'] is True
+    assert result['severity'] == 'high'
+    print("PASS: classify_update_major")
+
+
+def test_classify_update_no_change():
+    result = uc.classify_update("1.2.3", "1.2.3")
+    assert result is None
+    print("PASS: classify_update_no_change")
+
+
+def test_classify_update_multiple_major():
+    result = uc.classify_update("1.0.0", "3.0.0")
+    assert result is not None
+    assert result['update_type'] == 'major'
+    assert result['breaking_change'] is True
+    print("PASS: classify_update_multiple_major")
+
+
+def test_text_report_format():
+    updates = [{
+        'package': 'requests',
+        'installed': '2.28.0',
+        'latest': '2.31.0',
+        'update_type': 'minor',
+        'breaking_change': False,
+        'severity': 'medium',
+    }]
+    report = uc.generate_text_report(updates)
+    assert 'DEPENDENCY UPDATE REPORT' in report
+    assert 'requests' in report
+    assert '2.28.0' in report
+    assert '2.31.0' in report
+    assert 'MINOR' in report
+    assert 'MEDIUM' in report
+    print("PASS: text_report_format")
+
+
+def test_text_report_shows_breaking():
+    updates = [{
+        'package': 'flask',
+        'installed': '2.0.0',
+        'latest': '3.0.0',
+        'update_type': 'major',
+        'breaking_change': True,
+        'severity': 'high',
+    }]
+    report = uc.generate_text_report(updates)
+    assert 'BREAKING CHANGE' in report.upper() or '⚠' in report
+    print("PASS: text_report_shows_breaking")
+
+
+def test_json_report_structure():
+    updates = [
+        {
+            'package': 'pytest',
+            'installed': '8.0.0',
+            'latest': '8.2.0',
+            'update_type': 'minor',
+            'breaking_change': False,
+            'severity': 'medium',
+        },
+        {
+            'package': 'flask',
+            'installed': '2.0.0',
+            'latest': '3.0.0',
+            'update_type': 'major',
+            'breaking_change': True,
+            'severity': 'high',
+        }
+    ]
+    report_json = uc.generate_json_report(updates)
+    data = json.loads(report_json)
+    assert 'generated_at' in data
+    assert data['total_updates'] == 2
+    assert 'summary' in data
+    assert data['summary']['major'] == 1
+    assert data['summary']['minor'] == 1
+    assert data['summary']['breaking'] == 1
+    print("PASS: json_report_structure")
+
+
+def test_no_updates_report():
+    report = uc.generate_text_report([])
+    assert 'up to date' in report.lower() or 'all packages' in report.lower()
+    print("PASS: no_updates_report")
+
+
+def test_end_to_end_integration():
+    """End-to-end: check_updates with mocked data produces valid report."""
+    fake_installed = {
+        "test-pkg-old": "1.0.0",
+        "another-pkg": "2.5.3",
+    }
+    
+    def fake_get_latest(pkg):
+        if pkg == "test-pkg-old":
+            return "1.2.4"
+        elif pkg == "another-pkg":
+            return "3.0.0"
+        return None
+    
+    with patch('update_checker.get_installed_packages', return_value=fake_installed):
+        with patch('update_checker.get_latest_version', side_effect=fake_get_latest):
+            updates = uc.check_updates()
+    
+    assert len(updates) == 2
+    
+    test_pkg = next(u for u in updates if u['package'] == 'test-pkg-old')
+    assert test_pkg['update_type'] == 'minor'
+    assert test_pkg['breaking_change'] is False
+    
+    another = next(u for u in updates if u['package'] == 'another-pkg')
+    assert another['update_type'] == 'major'
+    assert another['breaking_change'] is True
+    
+    report = uc.generate_text_report(updates)
+    assert 'DEPENDENCY UPDATE REPORT' in report
+    assert 'MINOR' in report
+    assert 'BREAKING CHANGE' in report.upper()
+    
+    print(f"PASS: end_to_end_integration ({len(updates)} updates)")
+
+
+if __name__ == "__main__":
+    passed = 0
+    failed = 0
+    tests = [
+        test_parse_version,
+        test_classify_update_patch,
+        test_classify_update_minor,
+        test_classify_update_major,
+        test_classify_update_no_change,
+        test_classify_update_multiple_major,
+        test_text_report_format,
+        test_text_report_shows_breaking,
+        test_json_report_structure,
+        test_no_updates_report,
+        test_end_to_end_integration,
+    ]
+    for test_func in tests:
+        try:
+            test_func()
+            passed += 1
+        except AssertionError as e:
+            print(f"FAIL: {test_func.__name__} — {e}")
+            failed += 1
+        except Exception as e:
+            print(f"ERROR: {test_func.__name__} — {e}")
+            import traceback
+            traceback.print_exc()
+            failed += 1
+    print(f"\n{passed} passed, {failed} failed")
+    sys.exit(0 if failed == 0 else 1)