Update: The pull request mentioned below has been merged and motion-stump clears mocks automatically now, so this after block is no longer necessary.
This one had me "stumped" for awhile. When using motion-stump mocks, you need to clear them in an after block like this:
after do
Stump::Mocks.clear!
end
Someone has submitted a pull request to motion-stump for this to happen automatically but it hasn't been merged yet.