add tests for proxies' sources

- free (non auth) proxies' source

test/test_proxy_sources.py

@@ -0,0 +1,21 @@
+import unittest
+import sources
+
+
+class TestProxySources(unittest.TestCase):
+    def setUp(self):
+        self.proxies = {}
+
+    def test_get_proxies_from_all_sources(self):
+        sources_classes = sources.get_sources(auth=False)
+        for source_class in sources_classes:
+            source_instance = source_class()
+            if source_class.__name__ not in self.proxies:
+                self.proxies[source_class.__name__] = source_instance.get_proxies()
+        for source in self.proxies.keys():
+            # Assert that the total number of proxies retrieved is greater than zero
+            self.assertGreater(len(self.proxies[source]), 0)
+
+
+if __name__ == '__main__':
+    unittest.main()