Trac #25325: Feature check for benzene is broken

There is a mistake in the Benzene Features test: it should test for the
">>planar_code<<" string, not for ">>planar_graph<<". As it is now, the
test always fails.

URL: https://trac.sagemath.org/25325
Reported by: gh-antonio-rojas
Ticket author(s): Vincent Delecroix
Reviewer(s): Travis Scrimshaw

src/sage/features/graph_generators.py

@@ -110,7 +110,7 @@ class Benzene(Executable):
 
         sage: from sage.features.graph_generators import Benzene
         sage: Benzene().is_present()  # optional: benzene
-        True
+        FeatureTestResult('Benzene', True)
     """
     def __init__(self):
         r"""
@@ -130,7 +130,7 @@ def is_functional(self):
 
             sage: from sage.features.graph_generators import Benzene
             sage: Benzene().is_functional()  # optional: benzene
-            True
+            FeatureTestResult('Benzene', True)
         """
         devnull = open(os.devnull, 'wb')
         command = ["benzene", "2", "p"]
@@ -140,7 +140,7 @@ def is_functional(self):
             return FeatureTestResult(self, False,
                     reason="Call `{command}` failed with exit code {e.returncode}".format(command=" ".join(command), e=e))
 
-        expected = ">>planar_graph<<"
+        expected = ">>planar_code<<"
         if not lines.startswith(expected):
             return FeatureTestResult(self, False,
                     reason="Call `{command}` did not produce output that started with `{expected}`.".format(command=" ".join(command), expected=expected))