Add tests for downloadNfcFace endpoint

Add tests for /documents/{document_id}/nfc_face endpoint, added to the OpenAPI spec in onfido/onfido-openapi-spec@c479418

Author: DiogoAndreBotas

tests/conftest.py

@@ -57,12 +57,12 @@ def create_applicant(onfido_api, applicant_builder=None):
     return onfido_api.create_applicant(applicant_builder)
 
 
-def upload_document(onfido_api, applicant_id):
+def upload_document(onfido_api, applicant_id, file_path="tests/media/sample_driving_licence.png"):
     return onfido_api.upload_document(
         applicant_id=applicant_id,
         type=onfido.DocumentTypes.PASSPORT,
         side="front",
-        file="tests/media/sample_driving_licence.png",
+        file=file_path,
     )