Unmet expectations are ignored

[ods94065]

This appears to be a regression introduced in 0.4.6.

Consider this code:

import chai

class Foo(object):
    def foo(self):
        pass

class MyTest(chai.Chai):
    def testFoo(self):
        obj = Foo()
        self.expect(obj.foo).times(1)

As you can see, we never invoke obj.foo, so this test should fail. Yet, in Chai 0.4.6 it succeeds.

The culprit is the change in 0.4.6 to tear down stubs immediately after the test. Doing so clears stub._expectations – yet this also has the undesirable effect of clearing stub.unmet_expectations().