diff -r 4953c86af1bf Lib/idlelib/idle_test/test_io.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/idlelib/idle_test/test_io.py	Thu Mar 05 09:37:54 2015 +0200
@@ -0,0 +1,233 @@
+import unittest
+import io
+from idlelib.PyShell import PseudoInputFile, PseudoOutputFile
+
+
+class S(str):
+    def __str__(self):
+        return '%s:str' % type(self).__name__
+    def __unicode__(self):
+        return '%s:unicode' % type(self).__name__
+    def __len__(self):
+        return 3
+    def __iter__(self):
+        return iter('abc')
+    def __getitem__(self, *args):
+        return '%s:item' % type(self).__name__
+    def __getslice__(self, *args):
+        return '%s:slice' % type(self).__name__
+
+class MockShell:
+    def __init__(self):
+        self.reset()
+
+    def write(self, *args):
+        self.written.append(args)
+
+    def readline(self):
+        return self.lines.pop()
+
+    def close(self):
+        pass
+
+    def reset(self):
+        self.written = []
+
+    def push(self, lines):
+        self.lines = list(lines)[::-1]
+
+
+class PseudeOutputFilesTest(unittest.TestCase):
+    def test_misc(self):
+        shell = MockShell()
+        f = PseudoOutputFile(shell, 'stdout', 'utf-8')
+        self.assertIsInstance(f, io.TextIOBase)
+        self.assertEqual(f.encoding, 'utf-8')
+        self.assertIsNone(f.errors)
+        self.assertIsNone(f.newlines)
+        self.assertEqual(f.name, '<stdout>')
+        self.assertFalse(f.closed)
+        self.assertTrue(f.isatty())
+        self.assertFalse(f.readable())
+        self.assertTrue(f.writable())
+        self.assertFalse(f.seekable())
+
+    def test_unsupported(self):
+        shell = MockShell()
+        f = PseudoOutputFile(shell, 'stdout', 'utf-8')
+        self.assertRaises(OSError, f.fileno)
+        self.assertRaises(OSError, f.tell)
+        self.assertRaises(OSError, f.seek, 0)
+        self.assertRaises(OSError, f.read, 0)
+        self.assertRaises(OSError, f.readline, 0)
+
+    def test_write(self):
+        shell = MockShell()
+        f = PseudoOutputFile(shell, 'stdout', 'utf-8')
+        f.write('test')
+        self.assertEqual(shell.written, [('test', 'stdout')])
+        shell.reset()
+        f.write('t\xe8st')
+        self.assertEqual(shell.written, [('t\xe8st', 'stdout')])
+        shell.reset()
+
+        f.write(S('t\xe8st'))
+        self.assertEqual(shell.written, [('t\xe8st', 'stdout')])
+        self.assertEqual(type(shell.written[0][0]), str)
+        shell.reset()
+
+        self.assertRaises(TypeError, f.write)
+        self.assertEqual(shell.written, [])
+        self.assertRaises(TypeError, f.write, b'test')
+        self.assertRaises(TypeError, f.write, 123)
+        self.assertEqual(shell.written, [])
+        self.assertRaises(TypeError, f.write, 'test', 'spam')
+        self.assertEqual(shell.written, [])
+
+    def test_writelines(self):
+        shell = MockShell()
+        f = PseudoOutputFile(shell, 'stdout', 'utf-8')
+        f.writelines([])
+        self.assertEqual(shell.written, [])
+        shell.reset()
+        f.writelines(['one\n', 'two'])
+        self.assertEqual(shell.written,
+                         [('one\n', 'stdout'), ('two', 'stdout')])
+        shell.reset()
+        f.writelines(['on\xe8\n', 'tw\xf2'])
+        self.assertEqual(shell.written,
+                         [('on\xe8\n', 'stdout'), ('tw\xf2', 'stdout')])
+        shell.reset()
+
+        f.writelines([S('t\xe8st')])
+        self.assertEqual(shell.written, [('t\xe8st', 'stdout')])
+        self.assertEqual(type(shell.written[0][0]), str)
+        shell.reset()
+
+        self.assertRaises(TypeError, f.writelines)
+        self.assertEqual(shell.written, [])
+        self.assertRaises(TypeError, f.writelines, 123)
+        self.assertEqual(shell.written, [])
+        self.assertRaises(TypeError, f.writelines, [b'test'])
+        self.assertRaises(TypeError, f.writelines, [123])
+        self.assertEqual(shell.written, [])
+        self.assertRaises(TypeError, f.writelines, [], [])
+        self.assertEqual(shell.written, [])
+
+    def test_close(self):
+        shell = MockShell()
+        f = PseudoOutputFile(shell, 'stdout', 'utf-8')
+        self.assertFalse(f.closed)
+        f.write('test')
+        f.close()
+        self.assertTrue(f.closed)
+        self.assertRaises(ValueError, f.write, 'x')
+        self.assertEqual(shell.written, [('test', 'stdout')])
+        f.close()
+        self.assertRaises(TypeError, f.close, 1)
+
+
+class PseudeInputFilesTest(unittest.TestCase):
+    def test_misc(self):
+        shell = MockShell()
+        f = PseudoInputFile(shell, 'stdin', 'utf-8')
+        self.assertIsInstance(f, io.TextIOBase)
+        self.assertEqual(f.encoding, 'utf-8')
+        self.assertIsNone(f.errors)
+        self.assertIsNone(f.newlines)
+        self.assertEqual(f.name, '<stdin>')
+        self.assertFalse(f.closed)
+        self.assertTrue(f.isatty())
+        self.assertTrue(f.readable())
+        self.assertFalse(f.writable())
+        self.assertFalse(f.seekable())
+
+    def test_unsupported(self):
+        shell = MockShell()
+        f = PseudoInputFile(shell, 'stdin', 'utf-8')
+        self.assertRaises(OSError, f.fileno)
+        self.assertRaises(OSError, f.tell)
+        self.assertRaises(OSError, f.seek, 0)
+        self.assertRaises(OSError, f.write, 'x')
+        self.assertRaises(OSError, f.writelines, ['x'])
+
+    def test_read(self):
+        shell = MockShell()
+        f = PseudoInputFile(shell, 'stdin', 'utf-8')
+        shell.push(['one\n', 'two\n', ''])
+        self.assertEqual(f.read(), 'one\ntwo\n')
+        shell.push(['one\n', 'two\n', ''])
+        self.assertEqual(f.read(-1), 'one\ntwo\n')
+        shell.push(['one\n', 'two\n', ''])
+        self.assertEqual(f.read(None), 'one\ntwo\n')
+        shell.push(['one\n', 'two\n', 'three\n', ''])
+        self.assertEqual(f.read(2), 'on')
+        self.assertEqual(f.read(3), 'e\nt')
+        self.assertEqual(f.read(10), 'wo\nthree\n')
+
+        shell.push(['one\n', 'two\n'])
+        self.assertEqual(f.read(0), '')
+        self.assertRaises(TypeError, f.read, 1.5)
+        self.assertRaises(TypeError, f.read, '1')
+        self.assertRaises(TypeError, f.read, 1, 1)
+
+    def test_readline(self):
+        shell = MockShell()
+        f = PseudoInputFile(shell, 'stdin', 'utf-8')
+        shell.push(['one\n', 'two\n', 'three\n', 'four\n'])
+        self.assertEqual(f.readline(), 'one\n')
+        self.assertEqual(f.readline(-1), 'two\n')
+        self.assertEqual(f.readline(None), 'three\n')
+        shell.push(['one\ntwo\n'])
+        self.assertEqual(f.readline(), 'one\n')
+        self.assertEqual(f.readline(), 'two\n')
+        shell.push(['one', 'two', 'three'])
+        self.assertEqual(f.readline(), 'one')
+        self.assertEqual(f.readline(), 'two')
+        shell.push(['one\n', 'two\n', 'three\n'])
+        self.assertEqual(f.readline(2), 'on')
+        self.assertEqual(f.readline(1), 'e')
+        self.assertEqual(f.readline(1), '\n')
+        self.assertEqual(f.readline(10), 'two\n')
+
+        shell.push(['one\n', 'two\n'])
+        self.assertEqual(f.readline(0), '')
+        self.assertRaises(TypeError, f.readlines, 1.5)
+        self.assertRaises(TypeError, f.readlines, '1')
+        self.assertRaises(TypeError, f.readlines, 1, 1)
+
+    def test_readlines(self):
+        shell = MockShell()
+        f = PseudoInputFile(shell, 'stdin', 'utf-8')
+        shell.push(['one\n', 'two\n', ''])
+        self.assertEqual(f.readlines(), ['one\n', 'two\n'])
+        shell.push(['one\n', 'two\n', ''])
+        self.assertEqual(f.readlines(-1), ['one\n', 'two\n'])
+        shell.push(['one\n', 'two\n', ''])
+        self.assertEqual(f.readlines(None), ['one\n', 'two\n'])
+        shell.push(['one\n', 'two\n', ''])
+        self.assertEqual(f.readlines(0), ['one\n', 'two\n'])
+        shell.push(['one\n', 'two\n', ''])
+        self.assertEqual(f.readlines(3), ['one\n'])
+        shell.push(['one\n', 'two\n', ''])
+        self.assertEqual(f.readlines(4), ['one\n', 'two\n'])
+
+        shell.push(['one\n', 'two\n', ''])
+        self.assertRaises(TypeError, f.readlines, 1.5)
+        self.assertRaises(TypeError, f.readlines, '1')
+        self.assertRaises(TypeError, f.readlines, 1, 1)
+
+    def test_close(self):
+        shell = MockShell()
+        f = PseudoInputFile(shell, 'stdin', 'utf-8')
+        shell.push(['one\n', 'two\n', ''])
+        self.assertFalse(f.closed)
+        self.assertEqual(f.readline(), 'one\n')
+        f.close()
+        self.assertFalse(f.closed)
+        self.assertEqual(f.readline(), 'two\n')
+        self.assertRaises(TypeError, f.close, 1)
+
+
+if __name__ == '__main__':
+    unittest.main()