If the other changes you need me to make to the Manager still result in my raising different ValueErrors, as is currently the case, I'm OK to remove the prior `self.assertRaises`, but in that case I'd absolutely argue for the test checking the message being propagated was the correct one to inform the user why things broke in a non-opaque way.

If I can simplify the branching and flow such that only one meaningful exception is raised, then I could concede removing the `self.assertRaisesRegexp` in favour of the plain `self.assertRaises`.