feat: add test infrastructure and initial test coverage

[pdettori]

Summary

Phase 3 of repo orchestration — adds test infrastructure and coverage for previously untested critical paths.

New files:

• tests/__init__.py: package marker
• tests/conftest.py: shared mock_envoy_modules and mock_manager fixtures, eliminating duplication
• tests/test_tool_pre_invoke.py: 4 tests for getToolPreInvokeResponse (previously 0 coverage)
  • Allow with no modification
  • Allow with modified arguments forwarded
  • Block with violation details in MCP error response
  • Payload carries correct tool name
• tests/test_prompt_pre_fetch.py: 3 tests for getPromptPreFetchResponse (previously 0 coverage)
  • Allow with no modification
  • Allow with modified arguments forwarded
  • Block with MCP error response
• tests/test_helpers.py: 6 tests for helper functions (previously 0 coverage)
  • set_result_in_body: mutates and replaces arguments
  • get_modified_response: returns BodyResponse
  • create_mcp_immediate_error_response: default code, violation reason, mcp_error_code override

Test plan

• All 13 new tests pass locally
• All 9 existing tests in test_server.py still pass (no regressions)
• CI passes

uv run pytest tests/ -v

[evaline-ju]

Thanks for more tests, @pdettori ! I see that the conftest may have overlap with existing server tests https://github.com/kagenti/plugins-adapter/blob/main/tests/test_server.py . Perhaps we can help refactor usage with the conftest instead of duplication? It might be worth organizing the existing tests a bit for navigability since already existent "tool_post_invoke" tests aren't really discoverable w.r.t. these other "hook" (prompt_pre_fetch and tool_pre_invoke) new test files

[pdettori]

Thanks for the feedback @evaline-ju!

Both issues are addressed in the latest commit:

• CI lint failure: removed the unused import pytest from test_helpers.py (ruff F401)
• Fixture duplication / navigability: renamed test_server.py → test_tool_post_invoke.py so all hook tests now follow a consistent naming convention alongside test_tool_pre_invoke.py and test_prompt_pre_fetch.py. The three locally-duplicated fixtures (mock_envoy_modules, mock_manager, sample_tool_result_body) have been removed from that file and sample_tool_result_body promoted to conftest.py for shared use.

All 22 tests pass.

[pdettori]

Thanks for the feedback @evaline-ju!

Both issues are addressed in the latest commit:

• CI lint failure: removed the unused import pytest from test_helpers.py (ruff F401)
• Fixture duplication / navigability: renamed test_server.py → test_tool_post_invoke.py so all hook tests now follow a consistent naming convention alongside test_tool_pre_invoke.py and test_prompt_pre_fetch.py. The three locally-duplicated fixtures (mock_envoy_modules, mock_manager, sample_tool_result_body) have been removed from that file and sample_tool_result_body promoted to conftest.py for shared use.

All 22 tests pass.