'Ensure the header value is of type string or bytes as
per discussion in GH issue #3386'

def test_header_value_not_str(self, httpbin):

    headers_int = {'foo': 3}
    headers_dict = {'bar': {'foo': 'bar'}}
    headers_list = {'baz': ['foo', 'bar']}
    with pytest.raises(InvalidHeader):
        r = requests.get(httpbin('get'), headers=headers_int)
    with pytest.raises(InvalidHeader):
        r = requests.get(httpbin('get'), headers=headers_dict)
    with pytest.raises(InvalidHeader):
        r = requests.get(httpbin('get'), headers=headers_list)
