tests(amdsmi): [AILITOOLS-308] Create python mock testing suite

[amd-josnarlo]

Motivation

The Python suites that stub the amdsmi package installed fake modules into sys.modules and never restored them, so whichever suite ran next imported the stub and failed with ImportError: cannot import name 'AmdSmiRequiredCommandException' from 'amdsmi_cli_exceptions' (unknown location). The failure surfaced in an unrelated file and depended on discovery order, and the ad-hoc fixes applied so far left the same defect in three more classes with nothing to catch the next one. This groups the stubbing suites behind a single isolation contract and adds a guard that fails when any of them leaks.

Technical Details

Test harness (tests/python/common/common.py):

• Added ModuleIsolationMixin — snapshots the sys.modules names listed in ISOLATED_MODULES and the sys.path entry in ISOLATED_PATH during setUpClass, restores both in tearDownClass
• Added REPO_ROOT, resolved by walking up for amdsmi_cli/ + CMakeLists.txt; replaces the hard-coded ".." chains that needed editing on every directory move and silently SkipTested when off by one
• run_test_dir now exits 2 when discovery yields zero tests and no -k filter is set, instead of reporting success on an empty suite

Mock tier (tests/python/unit/mock/{gpu,system}/):

• Moved the seven suites that replace sys.modules entries under unit/mock/; the five that exercise the real library stay at unit/{gpu,system}/
• Refactored all seven onto ModuleIsolationMixin, removing three per-file constant names, two hand-rolled snapshot/restore shapes, and every local tearDownClass
• Closed the remaining leaks: TestCliMetricPartitionClock, TestCliMetricPartitionVirtualOS and TestVcnBusyNaviFallback never restored their amdsmi stubs; test_cli_set_clk_limit.py and test_output_file_stdin.py never removed their sys.path entry

Regression guard (tests/python/unit/test_module_isolation.py):

• New. Runs the mock tier in a nested runner, then asserts every declared module is restored to the identical object, no undeclared stub survives, and sys.path is unchanged

Docs (tests/python/README.md, docs/conceptual/test-design.md, CHANGELOG.md):

• Documented the unit/mock/ admission rule and the isolation contract a new suite must follow
• Scoped the C++ "mocking is a technique, not a separate test level" rule to C++ and explained why Python needs a containment boundary for process-wide sys.modules state

Issue Tracking

JIRA ID : AILITOOLS-308

Test Plan

Run unit_tests.py

Test Result

Test results return as expected

[therock-pr-bot]

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