Support for modifying string/bytes fields.

tests/abstract_test.py

@@ -0,0 +1,15 @@
+import pathlib
+import unittest
+
+
+class AbstractBlendFileTest(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.blendfiles = pathlib.Path(__file__).with_name('blendfiles')
+
+    def setUp(self):
+        self.bf = None
+
+    def tearDown(self):
+        if self.bf:
+            self.bf.close()