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[EDIT] FILE: test_replacer.py

from unittest import TestCase

from testfixtures import Replacer, ShouldRaise

class TestReplacer(TestCase):

def test_function(self):
        from testfixtures.tests import sample1
        assert sample1.z() == 'original z'

def test_z():
          return 'replacement z'

r = Replacer()
        r.replace('testfixtures.tests.sample1.z',test_z)

assert sample1.z() == 'replacement z'

r.restore()

assert sample1.z() == 'original z'

def test_class(self):
        from testfixtures.tests import sample1
        x = sample1.X()
        assert x.__class__.__name__ == 'X'

class XReplacement(sample1.X): pass

r = Replacer()
        r.replace('testfixtures.tests.sample1.X', XReplacement)

x = sample1.X()
        assert x.__class__.__name__ == 'XReplacement'
        assert sample1.X().y() == 'original y'

r.restore()

x = sample1.X()
        assert x.__class__.__name__ == 'X'

def test_method(self):
        from testfixtures.tests import sample1
        assert sample1.X().y() == 'original y'

def test_y(self):
          return 'replacement y'

r = Replacer()
        r.replace('testfixtures.tests.sample1.X.y',test_y)

assert sample1.X().y()[:38] == 'replacement y'

r.restore()

assert sample1.X().y() == 'original y'

def test_class_method(self):
        from testfixtures.tests import sample1
        c = sample1.X
        assert sample1.X.aMethod() is c

def rMethod(cls):
          return cls, 1

r = Replacer()
        r.replace('testfixtures.tests.sample1.X.aMethod',rMethod)

sample1.X.aMethod()
        assert sample1.X.aMethod() == (c, 1)

r.restore()

sample1.X.aMethod()
        assert sample1.X.aMethod() is c

def test_multiple_replace(self):
        from testfixtures.tests import sample1
        assert sample1.z() == 'original z'
        assert sample1.X().y() == 'original y'

def test_y(self):
          return self.__class__.__name__
        def test_z():
          return 'replacement z'

r = Replacer()
        r.replace('testfixtures.tests.sample1.z',test_z)
        r.replace('testfixtures.tests.sample1.X.y',test_y)

assert sample1.z() == 'replacement z'
        assert sample1.X().y() == 'X'

r.restore()

assert sample1.z() == 'original z'
        assert sample1.X().y() == 'original y'

def test_gotcha(self):
        # Just because you replace an object in one context:

from testfixtures.tests import sample1
        from testfixtures.tests import sample2
        assert sample1.z() == 'original z'

def test_z():
          return 'replacement z'

r = Replacer()
        r.replace('testfixtures.tests.sample1.z',test_z)

assert sample1.z() == 'replacement z'

# Doesn't meant that it's replaced in all contexts:

assert sample2.z() == 'original z'

r.restore()

def test_remove_called_twice(self):
        from testfixtures.tests import sample1

def test_z(): pass

r = Replacer()
        r.replace('testfixtures.tests.sample1.z',test_z)

r.restore()
        assert sample1.z() == 'original z'

def test_with_statement(self):
        from testfixtures.tests import sample1
        assert sample1.z() == 'original z'

def test_z():
          return 'replacement z'

with Replacer() as r:
            r.replace('testfixtures.tests.sample1.z',test_z)
            assert sample1.z() == 'replacement z'

assert sample1.z() == 'original z'

def test_not_there(self):
        def test_bad(): pass

with Replacer() as r:
            with ShouldRaise(AttributeError("Original 'bad' not found")):
                r.replace('testfixtures.tests.sample1.bad', test_bad)

CANCEL