Fix flaky tests in test_create_checkout and test_cmor_finder, improve test isolation in fre/make/tests

[Copilot]

Describe your changes

test_checkout_execute is flaky because it runs the checkout script with parallel mode (no_parallel_checkout=False), which generates shell-backgrounded git clone commands using bash-specific array syntax (pids+=()) under a #!/bin/sh shebang. This causes race conditions and shell compatibility failures depending on the CI environment.

Fix: Use no_parallel_checkout=True in test_checkout_execute since it tests the execute=True codepath, not parallel syntax (already covered by test_checkout_script_exists). Break assert all([...]) into individual assertions with messages for better failure diagnostics.

test_make_simple_varlist_deduplicates is flaky because it creates test files with different datetimes (19900101 and 19900201). make_simple_varlist uses iglob to pick one file non-deterministically, extracts its datetime, then globs for files matching that datetime. When iglob picks the 19900201 file first, the pattern *19900201*.nc only matches that one file, missing the salt file entirely.

Fix: Use the same datetime (19900101) for the duplicate temp file so the glob search pattern matches all files regardless of filesystem ordering.

Broader test isolation improvements across fre/make/tests/:

• New conftest.py — shared fixtures (checkout_out, compile_out, makefile_out) for TEST_BUILD_DIR env var management and output directory lifecycle
• test_create_compile.py — module-level shutil.rmtree/mkdir → @pytest.fixture(scope="module"); os.environ → monkeypatch.setenv()
• test_create_makefile.py — same module-level side effect removal
• test_run_fremake.py — same pattern; removed unused rmtree import

Known remaining patterns (out of scope for this PR): test-order dependencies across modules, network-dependent git clones, cleanup-as-test-function anti-pattern, shared ./tmp/ directory for container tests.

Issue ticket number and link (if applicable)

Checklist before requesting a review

• I ran my code
• I tried to make my code readable
• I tried to comment my code
• I wrote a new test, if applicable
• I wrote new instructions/documentation, if applicable
• I ran pytest and inspected it's output
• I ran pylint and attempted to implement some of it's feedback
• No print statements; all user-facing info uses logging module

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[ilaflott]

@copilot try again

[Copilot]

@copilot try again

Fixed in 8258e69. The CI failure was in test_make_simple_varlist_deduplicates — it created files with different datetimes (19900101 vs 19900201), but make_simple_varlist uses iglob to pick one file and builds a glob pattern from its datetime. When iglob picked the 19900201 file first, the pattern *19900201*.nc only matched that one file, missing the salt file entirely. Changed the duplicate to use the same datetime so all files are found regardless of filesystem ordering.

[ilaflott]

oh, right... 🙃