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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def assert_page_source_contains(self, expected_value, failure_message='Expected page source to contain: "{}"'):
 """ Asserts that the page source contains the string passed in expected_value """

        assertion = lambda: expected_value in self.driver_wrapper.page_source()
        self.webdriver_assert(assertion, unicode(failure_message).format(expected_value))