added test for empty return-data operation, like classification

test/fixtures/server.py

@@ -1,5 +1,6 @@
 import io
 import socket
+from collections import defaultdict
 from itertools import repeat
 from multiprocessing import Process
 from typing import Generator
@@ -72,7 +73,7 @@ def operation(core_operation):
 
 
 @pytest.fixture
-def core_operation(item_type, one_to_many):
+def core_operation(item_type, one_to_many, analysis_task):
     def upper(string: bytes):
         return string.decode().upper().encode()
 
@@ -84,6 +85,9 @@ def core_operation(item_type, one_to_many):
         im = Image.open(io.BytesIO(im))
         return image_to_bytes(im.rotate(90))
 
+    def classify(_: bytes):
+        return b""
+
     def stream_pages(pdf: bytes):
         for i, page in enumerate(fitz.open(stream=pdf)):
             # yield page.get_pixmap().tobytes("png"), metadata
@@ -92,15 +96,15 @@ def core_operation(item_type, one_to_many):
     try:
         d = {
             False: {
-                "string": upper,
-                "image": rotate,
+                "string": defaultdict(lambda: upper),
+                "image": {False: rotate, True: classify},
             },
             True: {
-                "string": duplicate,
-                "pdf": stream_pages,
+                "string": defaultdict(lambda: duplicate),
+                "pdf": defaultdict(lambda: stream_pages),
             },
         }
-        return d[one_to_many][item_type]
+        return d[one_to_many][item_type][analysis_task]
     except KeyError:
         return Nothing
 
@@ -115,6 +119,11 @@ def one_to_many(request):
     return request.param
 
 
+@pytest.fixture(params=[True, False])
+def analysis_task(request):
+    return request.param
+
+
 @pytest.fixture(params=[False, True])
 def batched(request):
     """Controls, whether the buffer processor function of the webserver is applied to batches or single items."""