feat: test coverage for extension_support/plugins module

[Vaishnav88sk]

PR Type

• Bug fix
• New feature
• Core Runtime change (higher bar -- see CONTRIBUTING.md)
• Docs / tooling
• Refactoring

Summary

Add unit test coverage for extension_support/plugins.py (15 tests).

Context / Motivation

The extension support plugin system is a critical part of Metaflow's architecture that allows third-party packages to extend Metaflow's functionality. Despite its importance, the plugin utility functions had zero test coverage.

Issue

Fixes #3163

Reproduction

Runtime:

Commands to run:

# paste exact commands

Where evidence shows up:

Before (error / log snippet)

paste here

After (evidence that fix works)

paste here

Root Cause

Why This Fix Is Correct

• All 15 new tests pass
• Tests use real Metaflow classes (RetryDecorator) to verify plugin loading
• Edge cases covered: empty lists, unknown categories, invalid paths

Failure Modes Considered

Changes Made

Added 15 tests covering:

• merge_lists: List merging with override behavior (5 tests)
• get_plugin_name: Name extraction for all plugin categories (6 tests)
• get_plugin: Plugin loading and error handling (2 tests)
• get_trampoline_cli_names: Trampoline CLI tracking (2 tests)

Tests

• Unit tests added/updated
• Reproduction script provided (required for Core Runtime)
• CI passes
• If tests are impractical: explain why below and provide manual evidence above

Non-Goals

AI Tool Usage

• No AI tools were used in this contribution
• AI tools were used (describe below)
  for formatting

[greptile-apps]

Greptile Summary

This PR adds 15 unit tests for extension_support/plugins.py covering merge_lists, get_plugin_name, get_plugin, and get_trampoline_cli_names. Most tests are straightforward and correctly exercise the production code, but a few have assertion gaps that reduce their diagnostic value.

Confidence Score: 4/5

Safe to merge; issues are test quality problems, not production regressions.

All findings are P2 test quality issues. The production code is unchanged. The one inline comment flags a set-based assertion that defeats its own purpose.

test/unit/test_extension_plugins.py — review assertion correctness in TestMergeLists and TestGetTrampolineCliNames.

Important Files Changed

Filename	Overview
test/unit/test_extension_plugins.py	New test file for extension_support/plugins.py; two tests have correctness problems already flagged in previous review rounds, and one additional test uses set-based deduplication that defeats its own "no duplicates" assertion.

_{Reviews (3): Last reviewed commit: "Merge branch 'master' into feat/add-exte..." | Re-trigger Greptile}

[romain-intel]

Great to add tests. Let's address the greptile and test comments and then I'll take a closer look.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (master@f357565). Learn more about missing BASE report.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #3166   +/-   ##
=========================================
  Coverage          ?   27.38%           
=========================================
  Files             ?      375           
  Lines             ?    51746           
  Branches          ?     9143           
=========================================
  Hits              ?    14170           
  Misses            ?    36675           
  Partials          ?      901           

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[Vaishnav88sk]

@romain-intel I've addressed the greptile bot's comments:

1. test_overrides_win_over_base now uses the same name "b" in both base and overrides, and verifies the override instance wins
2. test_contains_expected_entries now properly mocks _trampoline_cli_names before asserting

All 15 tests now pass with correct assertions. The branch has been force-pushed with the fixes.

[Vaishnav88sk]

@romain-intel