Add missing test for atomic update set method (#218)

Thanks @efagerberg for the patch!

tests/test_client.py

@@ -584,7 +584,7 @@ def test_add_with_boost(self):
         self.assertEqual(len(res), 5)
         self.assertEqual('doc_6', res.docs[0]['id'])
 
-    def test_field_update(self):
+    def test_field_update_inc(self):
         originalDocs = self.solr.search('doc')
         self.assertEqual(len(originalDocs), 3)
         updateList = []
@@ -601,6 +601,25 @@ def test_field_update(self):
             self.assertEqual(True, all(updatedDoc[k] == originalDoc[k] for k in updatedDoc.keys()
                                        if k not in ['_version_', 'popularity']))
 
+    def test_field_update_set(self):
+        originalDocs = self.solr.search('doc')
+        updated_popularity = 10
+        self.assertEqual(len(originalDocs), 3)
+        updateList = []
+        for i, doc in enumerate(originalDocs):
+            updateList.append({'id': doc['id'], 'popularity': updated_popularity})
+        self.solr.add(updateList, fieldUpdates={'popularity': 'set'})
+
+        updatedDocs = self.solr.search('doc')
+        self.assertEqual(len(updatedDocs), 3)
+        for i, (originalDoc, updatedDoc) in enumerate(zip(originalDocs, updatedDocs)):
+            self.assertEqual(len(updatedDoc.keys()), len(originalDoc.keys()))
+            self.assertEqual(updatedDoc['popularity'], updated_popularity)
+            # TODO: change this to use assertSetEqual:
+            self.assertEqual(True, all(updatedDoc[k] == originalDoc[k] for k in updatedDoc.keys()
+                                       if k not in ['_version_', 'popularity']))
+
+    def test_field_update_add(self):
         self.solr.add([
             {
                 'id': 'multivalued_1',