diff --git a/lib/xos-synchronizer/tests/test_scheduler.py b/lib/xos-synchronizer/tests/test_scheduler.py
new file mode 100644
index 0000000..afbf036
--- /dev/null
+++ b/lib/xos-synchronizer/tests/test_scheduler.py
@@ -0,0 +1,272 @@
+# Copyright 2017-present Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+from mock import patch
+import mock
+import pdb
+import networkx as nx
+
+import os
+import sys
+
+test_path = os.path.abspath(os.path.dirname(os.path.realpath(__file__)))
+sync_lib_dir = os.path.join(test_path, "..", "xossynchronizer")
+xos_dir = os.path.join(test_path, "..", "..", "..", "xos")
+
+class TestScheduling(unittest.TestCase):
+
+    __test__ = False
+
+    def setUp(self):
+        global mock_enumerator, event_loop
+
+        self.sys_path_save = sys.path
+        self.cwd_save = os.getcwd()
+
+        config = os.path.join(test_path, "test_config.yaml")
+        from xosconfig import Config
+
+        Config.clear()
+        Config.init(config, "synchronizer-config-schema.yaml")
+
+        from xossynchronizer.mock_modelaccessor_build import (
+            build_mock_modelaccessor,
+        )
+
+        build_mock_modelaccessor(sync_lib_dir, xos_dir, services_dir=None, service_xprotos=[])
+
+        os.chdir(os.path.join(test_path, ".."))  # config references tests/model-deps
+
+        import xossynchronizer.event_loop
+
+        reload(xossynchronizer.event_loop)
+        import xossynchronizer.backend
+
+        reload(xossynchronizer.backend)
+        from xossynchronizer.mock_modelaccessor import mock_enumerator
+        from xossynchronizer.modelaccessor import model_accessor
+
+        # import all class names to globals
+        for (k, v) in model_accessor.all_model_classes.items():
+            globals()[k] = v
+
+        b = xossynchronizer.backend.Backend()
+        steps_dir = Config.get("steps_dir")
+        self.steps = b.load_sync_step_modules(steps_dir)
+        self.synchronizer = xossynchronizer.event_loop.XOSObserver(self.steps)
+
+    def tearDown(self):
+        sys.path = self.sys_path_save
+        os.chdir(self.cwd_save)
+
+    def test_same_object_trivial(self):
+        s = Slice(pk=4)
+        t = Slice(pk=4)
+        same, t = self.synchronizer.same_object(s, t)
+        self.assertTrue(same)
+        self.assertEqual(t, event_loop.DIRECT_EDGE)
+
+    def test_same_object_trivial2(self):
+        s = Slice(pk=4)
+        t = Slice(pk=5)
+        same, t = self.synchronizer.same_object(s, t)
+        self.assertFalse(same)
+
+    def test_same_object_lst(self):
+        s = Slice(pk=5)
+        t = ControllerSlice(slice=s)
+        u = ControllerSlice(slice=s)
+
+        s.controllerslices = mock_enumerator([t, u])
+
+        same, et = self.synchronizer.same_object(s.controllerslices, u)
+        self.assertTrue(same)
+        self.assertEqual(et, event_loop.PROXY_EDGE)
+
+        same, et = self.synchronizer.same_object(s.controllerslices, t)
+
+        self.assertTrue(same)
+        self.assertEqual(et, event_loop.PROXY_EDGE)
+
+    def test_same_object_lst_dc(self):
+        r = Slice(pk=4)
+        s = Slice(pk=5)
+        t = ControllerSlice(slice=r)
+        u = ControllerSlice(slice=s)
+
+        s.controllerslices = mock_enumerator([u])
+
+        same, et = self.synchronizer.same_object(s.controllerslices, t)
+        self.assertFalse(same)
+
+        same, et = self.synchronizer.same_object(s.controllerslices, u)
+        self.assertTrue(same)
+
+    def test_concrete_path_no_model_path(self):
+        p = Port()
+        n = NetworkParameter()
+        verdict, _ = self.synchronizer.concrete_path_exists(p, n)
+        self.assertFalse(verdict)
+
+    def test_concrete_no_object_path_adjacent(self):
+        p = Instance()
+        s1 = Slice()
+        s2 = Slice()
+        p.slice = s2
+        verdict, _ = self.synchronizer.concrete_path_exists(p, s1)
+
+        self.assertFalse(verdict)
+
+    def test_concrete_object_path_adjacent(self):
+        p = Instance()
+        s = Slice()
+        p.slice = s
+        verdict, edge_type = self.synchronizer.concrete_path_exists(p, s)
+
+        self.assertTrue(verdict)
+        self.assertEqual(edge_type, event_loop.DIRECT_EDGE)
+
+    def test_concrete_object_controller_path_adjacent(self):
+        p = Instance()
+        q = Instance()
+        cs = ControllerSlice()
+        cs2 = ControllerSlice()
+        s1 = Slice()
+        s2 = Slice()
+        p.slice = s1
+        q.slice = s2
+        cs.slice = s1
+        s1.controllerslices = mock_enumerator([cs])
+        s2.controllerslices = mock_enumerator([])
+
+        verdict1, edge_type1 = self.synchronizer.concrete_path_exists(p, cs)
+        verdict2, _ = self.synchronizer.concrete_path_exists(q, cs)
+        verdict3, _ = self.synchronizer.concrete_path_exists(p, cs2)
+
+        self.assertTrue(verdict1)
+        self.assertFalse(verdict2)
+        self.assertFalse(verdict3)
+
+        self.assertEqual(edge_type1, event_loop.PROXY_EDGE)
+
+    def test_concrete_object_controller_path_distant(self):
+        p = Instance()
+        s = Slice()
+        t = Site()
+        ct = ControllerSite()
+        ct.site = t
+        p.slice = s
+        s.site = t
+        verdict = self.synchronizer.concrete_path_exists(p, ct)
+        self.assertTrue(verdict)
+
+    def test_concrete_object_path_distant(self):
+        p = Instance()
+        s = Slice()
+        t = Site()
+        p.slice = s
+        s.site = t
+        verdict = self.synchronizer.concrete_path_exists(p, t)
+        self.assertTrue(verdict)
+
+    def test_concrete_no_object_path_distant(self):
+        p = Instance()
+        s = Slice()
+        s.controllerslice = mock_enumerator([])
+
+        t = Site()
+        t.controllersite = mock_enumerator([])
+
+        ct = ControllerSite()
+        ct.site = Site()
+        p.slice = s
+        s.site = t
+
+        verdict, _ = self.synchronizer.concrete_path_exists(p, ct)
+        self.assertFalse(verdict)
+
+    def test_cohorting_independent(self):
+        i = Image()
+
+        p = Slice()
+        c = Instance()
+        c.slice = None
+        c.image = None
+
+        cohorts = self.synchronizer.compute_dependent_cohorts([i, p, c], False)
+        self.assertEqual(len(cohorts), 3)
+
+    def test_cohorting_related(self):
+        i = Image()
+        p = Port()
+        c = Instance()
+        c.image = i
+        s = ControllerSlice()
+
+        cohorts = self.synchronizer.compute_dependent_cohorts([i, p, c, s], False)
+        self.assertIn([i, c], cohorts)
+        self.assertIn([p], cohorts)
+        self.assertIn([s], cohorts)
+
+    def test_cohorting_related_multi(self):
+        i = Image()
+        p = Port()
+        c = Instance()
+        c.image = i
+        cs = ControllerSlice()
+        s = Slice()
+        cs.slice = s
+        s.controllerslices = mock_enumerator([cs])
+        c.slice = s
+
+        cohorts = self.synchronizer.compute_dependent_cohorts([i, p, c, s, cs], False)
+
+        big_cohort = max(cohorts, key=len)
+        self.assertGreater(big_cohort.index(c), big_cohort.index(i))
+        self.assertGreater(big_cohort.index(cs), big_cohort.index(s))
+        self.assertIn([p], cohorts)
+
+    def test_cohorting_related_multi_delete(self):
+        i = Image()
+        p = Port()
+        c = Instance()
+        c.image = i
+        cs = ControllerSlice()
+        s = Slice()
+        cs.slice = s
+        c.slice = s
+
+        cohorts = self.synchronizer.compute_dependent_cohorts([i, p, c, s, cs], True)
+
+        big_cohort = max(cohorts, key=len)
+        self.assertGreater(big_cohort.index(i), big_cohort.index(c))
+        self.assertGreater(big_cohort.index(s), big_cohort.index(cs))
+        self.assertIn([p], cohorts)
+
+    def test_cohorting_related_delete(self):
+        i = Image()
+        p = Port()
+        c = Instance()
+        c.image = i
+        s = ControllerSlice()
+
+        cohorts = self.synchronizer.compute_dependent_cohorts([i, p, c, s], True)
+        self.assertIn([c, i], cohorts)
+        self.assertIn([p], cohorts)
+        self.assertIn([s], cohorts)
+
+
+if __name__ == "__main__":
+    unittest.main()