Context for tests

test_context.py

# Inspired by http://stackoverflow.com/a/13875412

class ContextMixin(object):
    def setup_context(self):
        self._ctxs = []
        for cls in reversed(self.__class__.mro()):
            context_method = cls.__dict__.get('context')
            if context_method:
                ctx = context_method(self)
                self._ctxs.append(ctx)
        for ctx in self._ctxs:
            try:
                next(ctx)
            except TypeError:
                raise RuntimeError('{}.context() must yield'.format(cls.__name__))

    def teardown_context(self):
        for ctx in reversed(self._ctxs):
            for _ in ctx:
                raise RuntimeError('{}.context() must not yield more than once'.format(cls.__name__))

class A(ContextMixin):
    def context(self):
        print 'set up A'
        yield
        print 'tear down A'

class B(ContextMixin):
    def context(self):
        print 'set up B'
        yield
        print 'tear down B'

class C(object):
    pass

class Test(C, B, A):
    def context(self):
        print 'set up test'
        with open('/tmp/testfile', 'w') as f:
            self.f = f
            yield
        print 'tear down test'

test = Test()

test.setup_context()

print 'run test here', test.f

test.teardown_context()

"""
Output:

set up A
set up B
set up test
run test here <open file '/tmp/testfile', mode 'w' at 0x1109d48a0>
tear down test
tear down B
tear down A
"""