Assertion error for BytesIO object in Python unittest

I have a core logic classes like below:

class SomeDBTManifestProvider:

    def __init__(self):
        pass

    def extract_manifest_json(self, file_stream: BytesIO):
        try:
            zipf = zipfile.ZipFile(file_stream)
            manifest_json_text = [zipf.read(name) for name in zipf.namelist() if "/manifest.json" in name][0].decode("utf-8")
            return json.loads(manifest_json_text)
        except Exception as e:
            raise FetchManifestJsonException(e)


class DbtProvisioner(object):

    def __init__(self, dbt_manifest_provider: SomeDBTManifestProvider):
        self.dbt_manifest_provider = dbt_manifest_provider
        
    def provision(self, provision_request: ProvisionRequest):
        self.dbt_manifest_provider.extract_manifest_json(BytesIO(b'ABC'))
        return "Success"  

Where ProvisionRequest is nothing but a DataClass and it can be ignored for now. As it can be seen DbtProvisioner is dependent on SomeDBTManifestProvider, therefore I have used D.I to access the method of SomeDBTManifestProvider. Now, I want to test DbtProvisioner for which I wrote the below test case:

def test_dbt_provision(self):
        provision_request = ProvisionRequest(
            DataProduct("a", "b", "c", "d", "e", "f", {}, [{}]), Workload("ab", "cd", "ef", "gh", DbtAttr("path"))
        )
        dbt_manifest = Mock()
        actual = DbtProvisioner(dbt_manifest).provision(
            provision_request)
        dbt_manifest.extract_manifest_json.assert_called_with(BytesIO(b'ABC'))
        self.assertEqual("Success", actual)  

Now, using the above approach I want to ensure that my method has been called with the right set of arguments. But somehow, it is giving me the below error:

Expected: extract_manifest_json(<_io.BytesIO object at 0x10d675900>)
Actual: extract_manifest_json(<_io.BytesIO object at 0x10f8efef0>)

How do I resolve this error? What am I missing here?

I also referred to multiple articles from SO but didn't help in any way. TIA

The problem is that BytesIO objects do not compare to each other based on content, but identity, so while b'ABC' == b'ABC' is true, BytesIO(b'ABC') == BytesIO(b'ABC') is not because they are two different BytesIO objects.

To perform your test as desired, a workaround would be to use the getvalue method to extract the value of the BytesIO object used as the argument of the call, which can be found in the mock_calls attribute of the Mock object.

Change:

dbt_manifest.extract_manifest_json.assert_called_with(BytesIO(b'ABC'))

to:

self.assertEqual(dbt_manifest.extract_manifest_json.mock_calls[0].args[0].getvalue(), b'ABC'))