Revert "Remove MLTool unique unit test."

This reverts commit 5927a444.

arkindex/documents/tests/test_datasource.py

-from unittest.mock import MagicMock
 from django.test import TestCase
-from arkindex_common.ml_tool import MLTool, MLToolType
+from arkindex_common.ml_tool import MLToolType
 from arkindex.documents.models import DataSource
 
 
 class TestDataSource(TestCase):
 
-    @classmethod
-    def setUpTestData(cls):
-        cls.ml_tool = MagicMock(spec=MLTool)
-        cls.ml_tool.type = MLToolType.Recognizer
-        cls.ml_tool.slug = 'muddy'
-        cls.ml_tool.name = 'Muddy Recognizer'
-        cls.ml_tool.version = '0.42'
-
     def test_str(self):
         ds = DataSource(
             type=MLToolType.Classifier,