Source code for

# This file is part of Checkbox.
# Copyright 2012 Canonical Ltd.
# Written by:
#   Zygmunt Krynicki <>
# Checkbox is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 3,
# as published by the Free Software Foundation.

# Checkbox is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with Checkbox.  If not, see <>.

:mod:`` -- tools for testing IO

Implementation of context managers for observing IO

from io import StringIO
import sys

[docs]class TestIO: """ Helper class for capturing stdin, stdout, stderr IO for testing """ def __init__(self, *, input=None, combined=False): self._combined = combined self._input = input def __enter__(self): # Remember the real objects that we'll replace self._real_stdin = sys.stdin self._real_stdout = sys.stdout self._real_stderr = sys.stderr # Create fake objects. In combined mode the output is more similar to # what a user at a console would see (stdout and stderr are # intertwined) self._fake_stdin = StringIO(self._input) if self._combined: self._fake_combined = StringIO() else: self._fake_stdout = StringIO() self._fake_stderr = StringIO() # Stub-away .close() if self._combined: self._fake_combined.close = lambda: None else: self._fake_stdout.close = lambda: None self._fake_stderr.close = lambda: None # Lastly replace the real objects sys.stdin = self._fake_stdin if self._combined: sys.stdout = self._fake_combined sys.stderr = self._fake_combined else: sys.stdout = self._fake_stdout sys.stderr = self._fake_stderr return self def __exit__(self, *exc): # Save the data that was written to stdout and stderr if self._combined: self._test_combined = self._fake_combined.getvalue() else: self._test_stdout = self._fake_stdout.getvalue() self._test_stderr = self._fake_stderr.getvalue() # Close all fake streams self._fake_stdin.close() if self._combined: self._fake_combined.close() else: self._fake_stdout.close() self._fake_stderr.close() # And restore original streams sys.stdin = self._real_stdin sys.stdout = self._real_stdout sys.stderr = self._real_stderr @property def stdout(self): """ All stdout output """ return self._test_stdout @property def stderr(self): """ All stderr output """ return self._test_stderr @property def combined(self): """ All output combined from stdout and stderr """ return self._test_combined
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