add tests

tests/test_helpers.py

@@ -0,0 +1,24 @@
+# coding: utf-8
+# Copyright (c) Max-Planck-Institut für Eisenforschung GmbH - Computational Materials Design (CM) Department
+# Distributed under the terms of "New BSD License", see the LICENSE file.
+
+import unittest
+import numpy as np
+from ase.build import bulk
+import structuretoolkit as stk
+
+
+class TestHelpers(unittest.TestCase):
+    def test_get_cell(self):
+        self.assertEqual((3 * np.eye(3)).tolist(), stk.get_cell(3).tolist())
+        self.assertEqual(
+            ([1, 2, 3] * np.eye(3)).tolist(), stk.get_cell([1, 2, 3]).tolist()
+        )
+        atoms = bulk("Fe")
+        self.assertEqual(
+            atoms.cell.tolist(), stk.get_cell(atoms).tolist()
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()