add cycle unit test

awx/main/tests/unit/scheduler/test_dag_simple.py

@@ -0,0 +1,42 @@
+import pytest
+
+from awx.main.scheduler.dag_simple import SimpleDAG
+
+
+@pytest.fixture
+def node_generator():
+    def fn():
+        return object()
+    return fn
+
+
+@pytest.fixture
+def simple_cycle_1(node_generator):
+    g = SimpleDAG()
+    nodes = [node_generator() for i in range(4)]
+    map(lambda n: g.add_node(n), nodes)
+
+    r'''
+            0
+           /\
+          /  \
+         .    .
+         1---.2
+         .    |
+         |    |
+         -----|
+              .
+              3
+    '''
+    g.add_edge(nodes[0], nodes[1], "success_nodes")
+    g.add_edge(nodes[0], nodes[2], "success_nodes")
+    g.add_edge(nodes[2], nodes[3], "success_nodes")
+    g.add_edge(nodes[2], nodes[1], "success_nodes")
+    g.add_edge(nodes[1], nodes[2], "success_nodes")
+    return (g, nodes)
+
+
+def test_has_cycle(simple_cycle_1):
+    (g, nodes) = simple_cycle_1
+
+    assert g.has_cycle() is True