Comment 12 for bug 891186

You can only read and write bytes from cStringIO.StringIO, so the problem with this assertion is it's comparing bytes with unicode:

    fp.seek(0)
    self.assertThat(fp.read(), Contains(u'some unicode char (\xe1)'))

I'd write it instead asserting the UTF-8 byte string:

    self.assertThat(fp.getvalue() Contains("some unicode char (\xc3\xa1)"))

Or with `.decode("utf-8")` after the getvalue if you want to keep the unicode Contains which is neater, especially with older testtools versions.