Small example the how I'm using pytest

conftest,py

@pytest.fixture()
def foo_client(monkeypatch):
    def authenticate():
        pass
    monkeypatch.setattr(FooClient, "authenticate", authenticate)
    return FooClient("token", "secret")

test_foo.py

def test_add_data(foo_client):
    foo_client.add_data(["shuttlecloud.com"])
    assert "shuttlecloud.com" in foo_client.get_data()