Improved user-facing messages

tests/pending_manager_test.py

Index: tests/pending_manager_test.py
diff --git a/tests/pending_manager_test.py b/tests/pending_manager_test.py
index efef86f109eee3ce27deaafa82782c19fbd198f0..0407eae52bc6790daa4e402d2cd11a3c3571c3cc 100755
--- a/tests/pending_manager_test.py
+++ b/tests/pending_manager_test.py
@@ -165,19 +165,22 @@ class TestPendingManager(mocks.TestCase):
 
   def testNoVerification(self):
     try:
-      # Need at least one verification.
       self._get_pc([], [])
-      self.fail()
-    except AssertionError:
+    except ValueError:
       pass
+    else:
+      self.fail(msg='A PendingManager must require at least one verifier.')
+
     try:
       # Cannot have the same verifier two times.
       self._get_pc(
           [fake.FakeVerifier(base.SUCCEEDED)],
           [fake.FakeVerifier(base.SUCCEEDED)])
-      self.fail()
     except AssertionError:
       pass
+    else:
+      self.fail(msg='A PendingManager should not accept the same verifier'
+                ' two times.')
 
   def _check_1(self, pc, result):
     issue = 31337