These tests don't actually verify the expected driver "name". They also no longer verify all the other expected metadata fields since we've removed this line:
self.assertEqual(options.pool_options.metadata, metadata)

I'd suggest we change this test back to how it was and deal with the |c issue like this:

    async def test_metadata(self):
        if has_c():
            name = "PyMongo|c|async"
        else:
            name = "PyMongo|async"
        metadata = copy.deepcopy(_METADATA)
        metadata["driver"]["name"] = name
        metadata["application"] = {"name": "foobar"}
        client = self.simple_client("mongodb://foo:27017/?appname=foobar&connect=false")
        options = client.options
        self.assertEqual(options.pool_options.metadata, metadata)
        ...

We'll need to add the PyMongo|c|async string to synchro.py too.

These tests don't actually verify the expected driver "name".

You mean you don't like the assertIn or …

They also no longer verify all the other expected metadata fields since we've removed this line:
self.assertEqual(options.pool_options.metadata, metadata)

I updated _test_handshake to cover those.

Right, the new test only checks for a substring while the old test checks the whole thing.

Also the new _test_handshake is brittle since we need to update it every time we add a new field to the metadata.

So the old way is better imo.

Done, thanks! Much simpler, I agree. That leaves:

FAILED test/asynchronous/test_client.py::AsyncClientUnitTest::test_metadata - AssertionError: {'dri[19 chars]ongo|c|async|FooDriver', 'version': '4.10.0.de[167 chars]ar'}} != {'dri[19 chars]ongo|async|FooDriver', 'version': '4.10.0....
FAILED test/test_client.py::ClientUnitTest::test_metadata - AssertionError: {'dri[19 chars]ongo|c|FooDriver', 'version': '4.10.0.dev0|1.2[161 chars]ar'}} != {'dri[19 chars]ongo|FooDriver', 'version': '4.10.0.dev0|1...

So I'll add the same conditional for the FooDriver test.

We'll need to add the PyMongo|c|async string to synchro.py too.

Shouldn't we see a failure since it's not added there yet?

Hmm I suppose something is already translating PyMongo|c|async to PyMongo|c? Perhaps unasync does that already?

I was expecting to add a line here: https://github.com/mongodb/mongo-python-driver/blob/d0772f2/tools/synchro.py#L103

Yeah I don't understand why the tests pass with or without that string, maybe @blink1073 knows.

Synchro hadn't been run, it failed the static check: https://github.com/mongodb/mongo-python-driver/actions/runs/11023004771/job/30613463481?pr=1874#step:5:67