Add basic storage test 'storage-test.py'

tests/sandboxes/storage-test/original/bin/bash

+This is the original /bin/bash.

tests/sandboxes/storage-test/original/bin/hello

+This is the original /bin/hello.

tests/sandboxes/storage-test/overlay/bin/bash

+This is the replacement /bin/bash.
\ No newline at end of file

tests/sandboxes/storage-tests.py

+import os
+import pytest
+
+from buildstream._exceptions import ErrorDomain
+
+from buildstream._context import Context
+from buildstream.storage._casbaseddirectory import CasBasedDirectory
+from buildstream.storage._filebaseddirectory import FileBasedDirectory
+
+DATA_DIR = os.path.join(
+    os.path.dirname(os.path.realpath(__file__)),
+    "storage-test"
+)
+
+
+def setup_backend(backend_class, tmpdir):
+    if backend_class == FileBasedDirectory:
+        return backend_class(os.path.join(tmpdir, "vdir"))
+    else:
+        context = Context()
+        context.artifactdir = os.path.join(tmpdir, "cas")
+        return backend_class(context)
+
+
+@pytest.mark.parametrize("backend", [
+    FileBasedDirectory, CasBasedDirectory])
+@pytest.mark.datafiles(DATA_DIR)
+def test_import(tmpdir, datafiles, backend):
+    original = os.path.join(datafiles, "original")
+
+    c = setup_backend(backend, tmpdir)
+
+    c.import_files(original)
+
+    assert("bin/bash" in c.list_relative_paths())
+    assert("bin/hello" in c.list_relative_paths())
+
+
+@pytest.mark.parametrize("backend", [
+    FileBasedDirectory, CasBasedDirectory])
+@pytest.mark.datafiles(DATA_DIR)
+def test_modified_file_list(tmpdir, datafiles, backend):
+    original = os.path.join(datafiles, "original")
+    overlay = os.path.join(datafiles, "overlay")
+
+    c = setup_backend(backend, tmpdir)
+
+    c.import_files(original)
+
+    c.mark_unmodified()
+
+    c.import_files(overlay)
+
+    print("List of all paths in imported results: {}".format(c.list_relative_paths()))
+    assert("bin/bash" in c.list_relative_paths())
+    assert("bin/bash" in c.list_modified_paths())
+    assert("bin/hello" not in c.list_modified_paths())