bagit-gython is not thread safe

[djjuhasz]

When (*bagit.Bag).Validate() is run in two separate threads at the same time (e.g. via parallel tests) validation fails with a fatal Python error.

Test file

func TestValidateBag(t *testing.T) {
	t.Parallel()

	t.Run("Fails validation", func(t *testing.T) {
		t.Parallel()

		b, err := bagit.NewBagIt()
		assert.NilError(t, err)

		err = b.Validate("/tmp/691b8e7f-e6b7-41dd-bc47-868e2ff69333")
		assert.Error(t, err, "invalid: Expected bagit.txt does not exist: /tmp/691b8e7f-e6b7-41dd-bc47-868e2ff69333/bagit.txt")

		err = b.Cleanup()
		assert.NilError(t, err)
	})

	t.Run("Validates bag", func(t *testing.T) {
		t.Parallel()

		b, err := bagit.NewBagIt()
		assert.NilError(t, err)

		err = b.Validate("internal/testdata/valid-bag")
		assert.NilError(t, err)

		err = b.Cleanup()
		assert.NilError(t, err)
	})
}

Results

❯ go test ./...
?   	github.com/artefactual-labs/bagit-gython/internal/dist	[no test files]
?   	github.com/artefactual-labs/bagit-gython/internal/dist/data	[no test files]
?   	github.com/artefactual-labs/bagit-gython/internal/dist/generate	[no test files]
?   	github.com/artefactual-labs/bagit-gython/internal/runner	[no test files]
Unable to calculate file hashes for /home/djuhasz/Artefactual/artefactual-labs/bagit-gython/internal/testdata/valid-bag
Traceback (most recent call last):
  File "/tmp/python/bagit-bagit-lib-49db2197764d6aa1/bagit.py", line 890, in _validate_entries
    pool = multiprocessing.Pool(
           ^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/python/bagit-038d476ec7f987d3/lib/python3.12/multiprocessing/context.py", line 118, in Pool
    from .pool import Pool
  File "/tmp/python/bagit-038d476ec7f987d3/lib/python3.12/multiprocessing/pool.py", line 19, in <module>
    import queue
ModuleNotFoundError: No module named 'queue'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/tmp/python/bagit-bagit-lib-49db2197764d6aa1/bagit.py", line 895, in _validate_entries
    pool.terminate()
    ^^^^
UnboundLocalError: cannot access local variable 'pool' where it is not associated with a value
--- FAIL: TestValidateBag (0.00s)
    --- FAIL: TestValidateBag/Validates_bag (1.75s)
        bagit_test.go:34: assertion failed: error is not nil: invalid: cannot access local variable 'pool' where it is not associated with a value
FAIL
FAIL	github.com/artefactual-labs/bagit-gython	1.760s
FAIL

Additional information

If I remove one or more of the t.Parallel() calls from the test file, then the tests pass without error

[djjuhasz]

I also tried treating bagit.NewBagIt() as a singleton, by moving the constructor and cleanup to the main test function:

func TestValidateBag(t *testing.T) {
	t.Parallel()

	b, err := bagit.NewBagIt()
	assert.NilError(t, err)

	t.Cleanup(func() {
		err = b.Cleanup()
		assert.NilError(t, err)
	})

	t.Run("Fails validation", func(t *testing.T) {
		t.Parallel()

		err = b.Validate("/tmp/691b8e7f-e6b7-41dd-bc47-868e2ff69333")
		assert.Error(t, err, "invalid: Expected bagit.txt does not exist: /tmp/691b8e7f-e6b7-41dd-bc47-868e2ff69333/bagit.txt")
	})

	t.Run("Validates bag", func(t *testing.T) {
		t.Parallel()

		err = b.Validate("internal/testdata/valid-bag")
		assert.NilError(t, err)
	})
}

The tests passed in this case:

❯ go test ./...
?   	github.com/artefactual-labs/bagit-gython/internal/dist	[no test files]
?   	github.com/artefactual-labs/bagit-gython/internal/dist/data	[no test files]
?   	github.com/artefactual-labs/bagit-gython/internal/dist/generate	[no test files]
?   	github.com/artefactual-labs/bagit-gython/internal/runner	[no test files]
ok  	github.com/artefactual-labs/bagit-gython	1.819s