feat: add unit tests for report_generator.py (JSON, CSV, PDF, HTML)

[rthakkar0555]

Summary

Adds comprehensive pytest coverage for report_generator.py across all
4 supported output formats, closing issue #43.

---

Changes Made

tests/test_report_generator.py (new)

14 tests covering all formats:

JSON (4 tests)

• Output file is created at expected path
• Required keys present: scan_info, vulnerabilities, severity_counts
• severity_counts correctly tallies CRITICAL / HIGH / MEDIUM / LOW
• Empty vulnerability list produces valid JSON without crashing

CSV (4 tests)

• Output file is created
• Header row matches: ID, Severity, Package, Version, Title, CVSS, Status, Target, URL
• Vulnerability fields map to correct columns
• Empty input produces header-only CSV

PDF (3 tests)

• Output file is created
• Generated file is non-empty (size > 0)
• No exception raised on valid input

HTML (3 tests)

• Output file is created
• No {{ }} template placeholders remain in rendered output
• HTML special characters are escaped correctly (XSS prevention)

---

tests/conftest.py (updated)

Added two reusable fixtures:

• sample_vulnerabilities
• sample_scan_info

---

docksec/report_generator.py (bug fixes discovered during testing)

• Fixed fpdf2 cursor positioning crash — all multi_cell() calls
  now use new_x="LMARGIN", new_y="NEXT" as required by fpdf2 v2.8.7+
• Without this fix, PDF generation silently crashed in the existing code

docksec/config.py (bug fix discovered during testing)

• Wrapped langchain_core import in try/except to prevent
  pydantic_core import crash when AI features are not in use

---

Validation

pytest tests/test_report_generator.py -v
→ 14 passed, 0 failures

• All tests use tmp_path (no hardcoded paths)
• No real LLM or API calls made

Closes #43

[codecov-commenter]

Codecov Report

❌ Patch coverage is 86.57407% with 29 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@ca0eba7). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
docksec/report_generator.py	70.52%	28 Missing ⚠️
tests/conftest.py	88.88%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #85   +/-   ##
=======================================
  Coverage        ?   40.47%           
=======================================
  Files           ?       16           
  Lines           ?     1905           
  Branches        ?        0           
=======================================
  Hits            ?      771           
  Misses          ?     1134           
  Partials        ?        0           

Flag	Coverage Δ
unittests	40.47% <86.57%> (?)

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[advaitpatel]

lgtm. thank you for your contributions.