Increase covering coverage (#6099)

* Added Exception test to test_covering.py

* Completed Testing for covering.py

* Added test and style change

* Update networkx/algorithms/tests/test_covering.py

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

* Imported pytest, should pass all tests now

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

1 files changed, 11 insertions, 0 deletions

diff --git a/networkx/algorithms/tests/test_covering.py b/networkx/algorithms/tests/test_covering.py
index 40971963..b2f97a86 100644
--- a/networkx/algorithms/tests/test_covering.py
+++ b/networkx/algorithms/tests/test_covering.py
@@ -1,3 +1,5 @@
+import pytest
+
 import networkx as nx
 
 
@@ -13,6 +15,15 @@ class TestMinEdgeCover:
         G.add_edge(0, 0)
         assert nx.min_edge_cover(G) == {(0, 0)}
 
+    def test_graph_with_isolated_v(self):
+        G = nx.Graph()
+        G.add_node(1)
+        with pytest.raises(
+            nx.NetworkXException,
+            match="Graph has a node with no edge incident on it, so no edge cover exists.",
+        ):
+            nx.min_edge_cover(G)
+
     def test_graph_single_edge(self):
         G = nx.Graph([(0, 1)])
         assert nx.min_edge_cover(G) in ({(0, 1)}, {(1, 0)})