chore(test): skip the example plugin in default run-unit-tests runs

The example plugin is a skeleton - its unit test is a copy-paste
starting point for new plugins, not a real check. Running it as part
of `tox` / `tools/run-unit-tests` adds noise without signal.

Skip it by default via a SKIP_PLUGINS set. Explicit
`python tools/run-unit-tests example` still runs it so the template
stays verifiable.

Author: markuslf

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Fix `--require-hashes` pip install in pre-commit autoupdate workflow by using pinned version instead
 * tox.ini: disable the sdist build (`no_package = true`) so `tox` no longer trips over the flat top-level layout with "Multiple top-level packages discovered". The repo is a collection of plugin scripts, not a Python package
+* tools/run-unit-tests: skip the `example` plugin in default runs. Its unit test is a template meant to be copy-pasted into new plugins and does not correspond to a real check. Explicit `python tools/run-unit-tests example` still runs it
 * `.github/workflows/docs.yml`: pin all GitHub Actions by commit SHA (with the version as a trailing comment) instead of by tag, clearing the four OpenSSF Scorecard `PinnedDependenciesID` alerts. Dependabot is already configured for `github-actions` and updates hash-pinned actions natively
 * deb-updates: add missing `lib.txt` import so the "N update(s) available" summary no longer crashes with `AttributeError` at runtime
 * mysql-memory: fix `get_other_process_memory()` fallback path for psutil older than 5.3.0 (referenced an undefined `cmdline` variable and the wrong attribute on the process dict) and drop an unreachable `break` after `return` in `get_pfs_memory()`

tools/run-unit-tests

@@ -21,6 +21,11 @@ import os
 import subprocess
 import sys
 
+# Plugins whose unit tests exist only as a template and are not meant to
+# be executed by the runner. The `example` plugin is the reference skeleton
+# for new plugins, its unit test is a copy-paste starting point.
+SKIP_PLUGINS = {'example'}
+
 
 def main():
     """Find and run unit tests, report results."""
@@ -35,6 +40,10 @@ def main():
     for plugin in sorted(os.listdir(check_plugins)):
         if requested and plugin not in requested:
             continue
+        # when a plugin is explicitly requested on the command line, run it
+        # even if it is normally skipped; otherwise honor the skip set
+        if plugin in SKIP_PLUGINS and not requested:
+            continue
         unit_test_dir = os.path.join(check_plugins, plugin, 'unit-test')
         run_file = os.path.join(unit_test_dir, 'run')
         if os.path.isfile(run_file):