Add Tests for get_titles function

Added docstring for main.py script and updated it to only invoke update_titles
function if the file was run directly.
Added initial tests for titles updater script.

main.py

@@ -1,3 +1,7 @@
+'''
+    This script is used for changing the text below total members & live
+    members count in the developersIndia subreddit
+'''
 import praw
 import os
 import random
@@ -38,5 +42,5 @@ def update_titles():
     widgets.refresh()
     widgets.id_card.mod.update(subscribersText=titles[1])
 
-
-update_titles()
+if __name__ == '__main__':
+    update_titles()

test_titles_updater.py

@@ -0,0 +1,30 @@
+import unittest
+from unittest.mock import patch
+
+# patch out the environ dictionary
+# used to instantiate global variables in the titles_updater script
+# maybe move the call to os.environ in the script to the update_titles method?
+environ_patcher = patch.dict('os.environ', {
+    'REDDIT_CLIENT_ID': '',
+    'REDDIT_CLIENT_SECRET': '',
+    'REDDIT_PASSWORD': ''
+})
+environ_patcher.start()
+
+from main import get_titles
+
+# TODO: write tests for update_titles method after figuring out
+# which objects to mock and with what
+class TestTitlesUpdater(unittest.TestCase):
+    @patch('main.json.load', return_value={'titles': ['foo', 'bar', 'baz']})
+    def test_get_titles_returns_a_list(self, _):
+        titles = get_titles()
+        self.assertIsInstance(titles, list)
+
+    @patch('main.json.load', return_value={'titles': ['foo', 'bar', 'baz']})
+    def test_get_titles_contains_titles_from_dataset_file(self, mock_json_load):
+        titles = get_titles()
+
+        self.assertTrue(all(map(lambda title: title in mock_json_load.return_value['titles'], titles)))
+
+environ_patcher.stop()