Add xfail test for vulture bug.

tests/unit/scripts/test_run_vulture.py

@@ -138,3 +138,26 @@ def test_unused_method_camelcase(vultdir):
         Foo()
     """)
     assert not vultdir.run()
+
+
+@pytest.mark.xfail(
+    True, reason="https://bitbucket.org/jendrikseipp/vulture/issues/10/")
+def test_globals_bug(vultdir):
+    """Vulture has a bug where it detects globals as unused.
+
+    When this test starts XPASSing, we know it's been fixed.
+    """
+    vultdir.makepyfile(foo="""
+        import bar
+
+        bar.attr = True
+        bar.blub()
+    """)
+    vultdir.makepyfile(bar="""
+        attr = False
+
+        def blub():
+            if attr:
+                print("Hey!")
+    """)
+    assert not vultdir.run()