Testing methods that return nothing, XML, Python

Question

I'm trying to understand why, how, and if to unit test methods that seem to return nothing. I've read in a couple other threads that:

The point of a unit test is to test something that the function does. If its not returning a value, then what is it actually doing?

unittest for none type in python?

In my example, I am using the XMLSigner and XMLVerifier from the sign_XML library.

def verify_xml(signed_xml: str, cert_file: str) -> None:
    with open(cert_file, 'rb') as file:
        cert = file.read()
    with open(signed_xml, 'rb') as input_file:
        input_data = input_file.read()
    XMLVerifier().verify(input_data, x509_cert=cert)

I started looking up documentaion I found for SignXML. I read that verify():

class signxml.XMLVerifier Create a new XML Signature Verifier object, which can be used to hold configuration information and verify multiple pieces of data. verify(data, require_x509=True, x509_cert=None, cert_subject_name=None, ca_pem_file=None, ca_path=None, hmac_key=None, validate_schema=True, parser=None, uri_resolver=None, id_attribute=None, expect_references=1)

Verify the XML signature supplied in the data and return the XML node signed by the signature, or raise an exception if the signature is not valid. By default, this requires the signature to be generated using a valid X.509 certificate.

This is my first time working with this and I'm confused even more now. So this apparently does return something.

What I've attempted

For another method which ends up calling verify_xml I've used @patch and just checked that the method I patched was called and with the correct arguments. This also seems like it's not the way to do it, but I didn't know how else to test it.

It feels weird doing something similar with the verify_xml method and just checking that it has been called once.

I've also tried self.assertIsNone... and that passes but that seems weird to me and not like it's a way one does this.

Could someone help me understand why, how, and if to unit test methods that seem to return nothing).

Thanks

Gang · Answer 1 · 2018-04-12T23:52:32.833

to test verify_xml() is to test the Exception triggered by XMLVerifer().verify() if input parameters is not valid

There are a few types of exceptions you can tested.

from signxml import (XMLSigner, XMLVerifier, InvalidInput, InvalidSignature, InvalidCertificate, InvalidDigest)


class TestVerifyXML(unittest.TestCase):

    def setUpCls(cls):
        cls.signed_xml = from_magic()
        cls.cert_file = from_magic2()
        cls.ceft_file_bad = from_magic_bad() 

    def test_verify_xml(self):

        # no Exception with correct xml
        verify_xml(self.signed_xml, self.cert_file)

        with self.assertRaises(InvalidSignature):
            verify_xml(self.signed_xml, self.cert_file_bad)

Testing methods that return nothing, XML, Python

1 Answers1