[Test Improver] test: expand update command coverage (3 -> 20 tests)

[danielmeppiel]

🤖 This is an automated PR from Test Improver, an AI assistant focused on improving tests.

Goal and Rationale

update.py had only 3 tests covering the happy-path Windows and Unix install flows, leaving 7 distinct code paths completely untested. This PR adds 17 tests to cover the remaining paths, focusing on error conditions and guard logic that could hide real bugs.

Approach

Added two new test classes alongside the existing TestUpdateCommand:

• TestUpdateHelpers — unit tests for the 4 platform-detection helper functions (_get_update_installer_url, _get_update_installer_suffix, _get_installer_run_command). These are pure functions that are easy to test in isolation.
• Extended TestUpdateCommand — integration-style tests using CliRunner for the main command paths.

Newly covered paths

Scenario	Previously	Now
Dev version (unknown) without --check	Untested	Covered
Dev version (unknown) with --check	Untested	Covered
Version fetch returns None	Untested	Covered
Already on latest version	Untested	Covered
--check when update is available	Untested	Covered
Installer subprocess returns non-zero	Untested	Covered
requests not importable (ImportError)	Untested	Covered
Download raises generic exception	Untested	Covered
Unix manual update command	Untested	Covered
Helper: URL per platform	Untested	Covered
Helper: suffix per platform	Untested	Covered
Helper: run-command /bin/sh fallback	Untested	Covered
Helper: run-command pwsh fallback	Untested	Covered
Helper: raises when PowerShell missing	Untested	Covered

Coverage Impact

File	Before	After
src/apm_cli/commands/update.py	~25% (3 tests)	~90%+ (20 tests)

Trade-offs

• All tests mock network and subprocess calls — no live I/O.
• Platform detection is patched via patch.object(sys, "platform", ...) consistent with existing tests.

Test Status

All 3124 unit tests pass:

3124 passed in 15.33s

Reproducibility

uv run pytest tests/unit/test_update_command.py -v
uv run pytest tests/unit tests/test_console.py -x -q

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