How to use the mike.git_utils.read_file function in mike

def test_nonexistent_file(self):
        self.assertRaises(git_utils.GitError, git_utils.read_file, 'branch',
                          'nonexist.txt')

def test_read_file(self):
        self.assertEqual(git_utils.read_file('branch', 'file.txt'),
                         b'this is some text')

def test_read_file_as_text(self):
        self.assertEqual(git_utils.read_file('branch', 'file.txt',
                                             universal_newlines=True),
                         'this is some text')

def list_versions(branch='gh-pages'):
    try:
        return Versions.loads(git_utils.read_file(
            branch, versions_file, universal_newlines=True
        ))
    except git_utils.GitError:
        return Versions()

def do_GET(self):
        path = self.send_headers()
        if path is not None:
            body = git_utils.read_file(self.branch, path)
            self.wfile.write(body)