How to use the coverage.backward.StringIO function in coverage

def test_plugin2_with_text_report(self):
        self.make_render_and_caller()

        cov = coverage.Coverage(branch=True, omit=["*quux*"])
        cov.set_option("run:plugins", ["tests.plugin2"])

        self.start_import_stop(cov, "caller")

        repout = StringIO()
        total = cov.report(file=repout, include=["*.html"], omit=["uni*.html"], show_missing=True)
        report = repout.getvalue().splitlines()
        expected = [
            'Name         Stmts   Miss Branch BrPart  Cover   Missing',
            '--------------------------------------------------------',
            'bar_4.html       4      2      0      0    50%   1, 4',
            'foo_7.html       7      5      0      0    29%   1-3, 6-7',
            '--------------------------------------------------------',
            'TOTAL           11      7      0      0    36%',
            ]
        self.assertEqual(expected, report)
        self.assertAlmostEqual(total, 36.36, places=2)

def f1_debug_output(self, debug):
        """Runs some code with `debug` option, returns the debug output."""
        # Make code to run.
        self.make_file("f1.py", """\
            def f1(x):
                return x+1

            for i in range(5):
                f1(i)
            """)

        debug_out = StringIO()
        cov = coverage.Coverage(debug=debug)
        cov._debug_file = debug_out
        self.start_import_stop(cov, "f1")
        cov.save()

        out_lines = debug_out.getvalue()
        return out_lines

def get_report(self, cov):
        """Get the report from `cov`, and canonicalize it."""
        repout = StringIO()
        cov.report(file=repout, show_missing=False)
        report = repout.getvalue().replace('\\', '/')
        report = re.sub(r" +", " ", report)
        return report

""")
        self.make_file(".coveragerc", """\
            [run]
            parallel = True
            source = .
            """)

        cov = coverage.Coverage(source=None, branch=None, config_file='.coveragerc')
        if append:
            cov.load()
        else:
            cov.erase()
        self.start_import_stop(cov, "prog")
        cov.combine()
        cov.save()
        report = StringIO()
        cov.report(show_missing=None, ignore_errors=True, file=report, skip_covered=None,
                   skip_empty=None)
        self.assertEqual(report.getvalue(), textwrap.dedent("""\
            Name      Stmts   Miss  Cover
            -----------------------------
            prog.py       4      1    75%
            """))
        self.assert_file_count(".coverage", 0)
        self.assert_file_count(".coverage.*", 1)

def setUp(self):
        super(StdStreamCapturingMixin, self).setUp()

        # Capture stdout and stderr so we can examine them in tests.
        # nose keeps stdout from littering the screen, so we can safely Tee it,
        # but it doesn't capture stderr, so we don't want to Tee stderr to the
        # real stderr, since it will interfere with our nice field of dots.
        old_stdout = sys.stdout
        self.captured_stdout = StringIO()
        sys.stdout = Tee(sys.stdout, self.captured_stdout)

        old_stderr = sys.stderr
        self.captured_stderr = StringIO()
        sys.stderr = self.captured_stderr

        self.addCleanup(self.cleanup_std_streams, old_stdout, old_stderr)

def coverage_usepkgs(self, **kwargs):
        """Try coverage.report()."""
        cov = coverage.Coverage()
        cov.start()
        import usepkgs  # pragma: nested   # pylint: disable=import-error, unused-variable
        cov.stop()      # pragma: nested
        report = StringIO()
        cov.report(file=report, **kwargs)
        return report.getvalue()

The arguments are tuples: (name, value) for Coverage.set_option.
        """
        self.make_rigged_file("file1.py", 339, 155)
        self.make_rigged_file("file2.py", 13, 3)
        self.make_rigged_file("file3.py", 234, 228)
        self.make_file("doit.py", "import file1, file2, file3")

        cov = Coverage(source=["."], omit=["doit.py"])
        cov.start()
        import doit             # pragma: nested # pylint: disable=import-error, unused-import
        cov.stop()              # pragma: nested
        for name, value in options:
            cov.set_option(name, value)
        printer = SummaryReporter(cov)
        destination = StringIO()
        printer.report([], destination)
        return destination.getvalue()

def get_report(self, cov):
        """Get the report from `cov`, and canonicalize it."""
        repout = StringIO()
        cov.report(file=repout, show_missing=False)
        report = repout.getvalue().replace('\\', '/')
        report = re.sub(r" +", " ", report)
        return report