Fix unit tests

diagrams/__init__.py

@@ -17,10 +17,7 @@ __cluster = contextvars.ContextVar("cluster")
 
 
 def getdiagram():
-    try:
-        return __diagram.get()
-    except LookupError:
-        raise EnvironmentError("Global diagrams context not set up")
+    return __diagram.get()
 
 
 def setdiagram(diagram):
@@ -53,7 +50,7 @@ class _Cluster:
 
         try:
             self._parent = getcluster() or getdiagram()
-        except EnvironmentError:
+        except LookupError:
             self._parent = None
 
     
@@ -348,6 +345,8 @@ class Node(_Cluster):
         self._attrs.update(attrs)
 
         # If a node is in the cluster context, add it to cluster.
+        if not self._parent:
+            raise EnvironmentError("Global diagrams context not set up")
         self._parent.node(self)
 
     def __enter__(self):

tests/test_diagram.py

@@ -135,20 +135,20 @@ class ClusterTest(unittest.TestCase):
 
     def test_with_global_context(self):
         with Diagram(name=os.path.join(self.name, "with_global_context"), show=False):
-            self.assertIsNone(getcluster())
+            self.assertEqual(getcluster(), getdiagram())
             with Cluster():
-                self.assertIsNotNone(getcluster())
-            self.assertIsNone(getcluster())
+                self.assertNotEqual(getcluster(), getdiagram())
+            self.assertEqual(getcluster(), getdiagram())
 
     def test_with_nested_cluster(self):
         with Diagram(name=os.path.join(self.name, "with_nested_cluster"), show=False):
-            self.assertIsNone(getcluster())
+            self.assertEqual(getcluster(), getdiagram())
             with Cluster() as c1:
                 self.assertEqual(c1, getcluster())
                 with Cluster() as c2:
                     self.assertEqual(c2, getcluster())
                 self.assertEqual(c1, getcluster())
-            self.assertIsNone(getcluster())
+            self.assertEqual(getcluster(), getdiagram())
 
     def test_node_not_in_diagram(self):
         # Node must be belong to a diagrams.