rename test image method

tracim/tests/__init__.py

     assert content_query.count() > 0
 
 
-def create_test_image():
+def create_1000px_png_test_image():
     file = BytesIO()
     image = Image.new('RGBA', size=(1000, 1000), color=(0, 0, 0))
     image.save(file, 'png')

tracim/tests/functional/test_contents.py

 from tracim.models.data import ContentType
 from tracim.models import get_tm_session
 from tracim.models.revision_protection import new_revision
-from tracim.tests import FunctionalTest, create_test_image
+from tracim.tests import FunctionalTest
+from tracim.tests import create_1000px_png_test_image
 from tracim.tests import set_html_document_slug_to_legacy
 from tracim.fixtures.content import Content as ContentFixtures
 from tracim.fixtures.users_and_groups import Base as BaseFixture
         dbsession.flush()
         transaction.commit()
         content_id = int(test_file.content_id)
-        image = create_test_image()
+        image = create_1000px_png_test_image()
         self.testapp.authorization = (
             'Basic',
             (
         dbsession.flush()
         transaction.commit()
         content_id = int(test_file.content_id)
-        image = create_test_image()
+        image = create_1000px_png_test_image()
         self.testapp.authorization = (
             'Basic',
             (
         dbsession.flush()
         transaction.commit()
         content_id = int(test_file.content_id)
-        image = create_test_image()
+        image = create_1000px_png_test_image()
         self.testapp.authorization = (
             'Basic',
             (
         dbsession.flush()
         transaction.commit()
         content_id = int(test_file.content_id)
-        image = create_test_image()
+        image = create_1000px_png_test_image()
         self.testapp.authorization = (
             'Basic',
             (
         transaction.commit()
         content_id = int(test_file.content_id)
         revision_id = int(test_file.revision_id)
-        image = create_test_image()
+        image = create_1000px_png_test_image()
         self.testapp.authorization = (
             'Basic',
             (
         dbsession.flush()
         transaction.commit()
         content_id = int(test_file.content_id)
-        image = create_test_image()
+        image = create_1000px_png_test_image()
         self.testapp.authorization = (
             'Basic',
             (
         transaction.commit()
         content_id = int(test_file.content_id)
         revision_id = int(test_file.revision_id)
-        image = create_test_image()
+        image = create_1000px_png_test_image()
         self.testapp.authorization = (
             'Basic',
             (