couple of more unit tests

Author: ciur

tests/test_engine.py

@@ -4,4 +4,4 @@
 def test_engine():
     engine = create_engine('solr://solr-instance.default')
     assert engine.url.scheme == 'solr'
-    assert str(engine.url.scheme) == 'solr'
+    assert str(engine.url.scheme.value) == 'solr'

tests/test_index.py

@@ -0,0 +1,8 @@
+from salinic.engine import create_engine
+from salinic.index import get_ro_client_backend_class
+
+
+def test_get_ro_client_backend_class():
+    url = "solr://solr-solrcloud-0.solr-solrcloud-headless.default"
+    engine = create_engine(url)
+    assert get_ro_client_backend_class(engine)