Update DocumentVersionSignatureCreateForm

Use FilteredSelectionForm. Improve document signatures tests.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/document_signatures/tests/mixins.py

@@ -0,0 +1,22 @@
+from __future__ import absolute_import, unicode_literals
+
+from django.core.files import File
+
+from mayan.apps.django_gpg.models import Key
+
+from ..models import DetachedSignature
+
+from .literals import TEST_KEY_FILE, TEST_SIGNATURE_FILE_PATH
+
+
+class SignaturesTestMixin(object):
+    def _create_detached_signature(self):
+        with open(TEST_SIGNATURE_FILE_PATH, mode='rb') as file_object:
+            self.test_signature = DetachedSignature.objects.create(
+                document_version=self.document.latest_version,
+                signature_file=File(file_object)
+            )
+
+    def _create_test_key(self):
+        with open(TEST_KEY_FILE, mode='rb') as file_object:
+            self.test_key = Key.objects.create(key_data=file_object.read())