def test_file(self):
        '''
        Check that File.copy yields the proper content in the destination file
        in all situations that trigger different code paths:
        - different content
        - different content of the same size
        - same content
        - long content
        '''
        src = self.tmppath('src')
        dest = self.tmppath('dest')

        for content in samples:
            with open(src, 'wb') as tmp:
                tmp.write(content)
            # Ensure the destination file, when it exists, is older than the
            # source
            if os.path.exists(dest):
                time = os.path.getmtime(src) - 1
                os.utime(dest, (time, time))
            f = File(src)
            f.copy(dest)
            self.assertEqual(content, open(dest, 'rb').read())
            self.assertEqual(content, f.open().read())
            self.assertEqual(content, f.open().read())

    def test_file_open(self):
        '''
        Test whether File.open returns an appropriately reset file object.
        '''
        src = self.tmppath('src')
        content = ''.join(samples)
        with open(src, 'wb') as tmp:
            tmp.write(content)

        f = File(src)
        self.assertEqual(content[:42], f.open().read(42))
        self.assertEqual(content, f.open().read())

    def test_file_dest(self):
        '''
        Similar to test_file, but for a destination object instead of
        a destination file. This ensures the destination object is being
        used properly by File.copy, ensuring that other subclasses of Dest
        will work.
        '''
        src = self.tmppath('src')
        dest = MockDest()

        for content in samples:
            with open(src, 'wb') as tmp:
                tmp.write(content)
            f = File(src)
            f.copy(dest)
            self.assertEqual(content, dest.getvalue())

    def test_file_no_write(self):
        '''
        Test various conditions where File.copy is expected not to write
        in the destination file.
        '''
        src = self.tmppath('src')
        dest = self.tmppath('dest')

        with open(src, 'wb') as tmp:
            tmp.write('test')

        # Initial copy
        f = File(src)
        f.copy(dest)

        # Ensure subsequent copies won't trigger writes
        f.copy(DestNoWrite(dest))
        self.assertEqual('test', open(dest, 'rb').read())

        # When the source file is newer, but with the same content, no copy
        # should occur
        time = os.path.getmtime(src) - 1
        os.utime(dest, (time, time))
        f.copy(DestNoWrite(dest))
        self.assertEqual('test', open(dest, 'rb').read())

        # When the source file is older than the destination file, even with
        # different content, no copy should occur.
        with open(src, 'wb') as tmp:
            tmp.write('fooo')
        time = os.path.getmtime(dest) - 1
        os.utime(src, (time, time))
        f.copy(DestNoWrite(dest))
        self.assertEqual('test', open(dest, 'rb').read())

        # Double check that under conditions where a copy occurs, we would get
        # an exception.
        time = os.path.getmtime(src) - 1
        os.utime(dest, (time, time))
        self.assertRaises(RuntimeError, f.copy, DestNoWrite(dest))