testCMFCategory: update test that was testing nothing

Before the change testing the value set for category membership,
"p1.setCareerSubordination(o1)" was not raising, making this test
useless in reality. With the change, this now raises, but with a
different message.

product/CMFCategory/tests/testCMFCategory.py

@@ -807,12 +807,12 @@ class TestCMFCategory(ERP5TypeTestCase):
     else:
       o1 = organisation_module._getOb(self.id1)
 
-    try:
-      p1.setCareerSubordination(o1)
-    except Exception, e:
-      self.assertTrue(isinstance(e, TypeError))
-      self.assertEqual(e.args[0], 'Category must be of string, tuple of '
-                                  'string or list of string type.')
+    self.assertRaisesRegexp(
+      TypeError,
+      'This method only takes a string or an iterable of strings as parameter.',
+      p1.setCareerSubordination,
+      o1
+    )
 
   def test_23_getCategoryChildValueList(self):
     pc = self.getCategoriesTool()