Tools/Scripts/webkitpy/common/system/outputcapture.py

# Copyright (c) 2009, Google Inc. All rights reserved.
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# modification, are permitted provided that the following conditions are
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# Class for unittest support.  Used for capturing stderr/stdout.

import sys
import unittest
from StringIO import StringIO

class OutputCapture(object):
    def __init__(self):
        self.saved_outputs = dict()

    def _capture_output_with_name(self, output_name):
        self.saved_outputs[output_name] = getattr(sys, output_name)
        captured_output = StringIO()
        setattr(sys, output_name, captured_output)
        return captured_output

    def _restore_output_with_name(self, output_name):
        captured_output = getattr(sys, output_name).getvalue()
        setattr(sys, output_name, self.saved_outputs[output_name])
        del self.saved_outputs[output_name]
        return captured_output

    def capture_output(self):
        return (self._capture_output_with_name("stdout"), self._capture_output_with_name("stderr"))

    def restore_output(self):
        return (self._restore_output_with_name("stdout"), self._restore_output_with_name("stderr"))

    def assert_outputs(self, testcase, function, args=[], kwargs={}, expected_stdout="", expected_stderr="", expected_exception=None):
        self.capture_output()
        if expected_exception:
            return_value = testcase.assertRaises(expected_exception, function, *args, **kwargs)
        else:
            return_value = function(*args, **kwargs)
        (stdout_string, stderr_string) = self.restore_output()
        testcase.assertEqual(stdout_string, expected_stdout)
        testcase.assertEqual(stderr_string, expected_stderr)
        # This is a little strange, but I don't know where else to return this information.
        return return_value


class OutputCaptureTestCaseBase(unittest.TestCase):
    def setUp(self):
        unittest.TestCase.setUp(self)
        self.output_capture = OutputCapture()
        (self.__captured_stdout, self.__captured_stderr) = self.output_capture.capture_output()

    def tearDown(self):
        del self.__captured_stdout
        del self.__captured_stderr
        self.output_capture.restore_output()
        unittest.TestCase.tearDown(self)

    def assertStdout(self, expected_stdout):
        self.assertEquals(expected_stdout, self.__captured_stdout.getvalue())

    def assertStderr(self, expected_stderr):
        self.assertEquals(expected_stderr, self.__captured_stderr.getvalue())