diff --git a/test/fixtures/input.py b/test/fixtures/input.py
index 9562159..a9bd2a0 100644
--- a/test/fixtures/input.py
+++ b/test/fixtures/input.py
@@ -3,12 +3,13 @@ from itertools import starmap, repeat
 import numpy as np
 import pytest
 from PIL import Image
-from funcy import lmap, compose, flatten
+from funcy import lmap, compose, flatten, lflatten
 
 from pyinfra.server.dispatcher.dispatcher import Nothing
 from pyinfra.server.utils import pack, unpack, normalize_item
 from pyinfra.utils.func import star, lift, lstarlift
 from test.utils.image import image_to_bytes
+from test.utils.server import string_to_bytes
 
 
 @pytest.fixture
@@ -32,9 +33,22 @@ def input_data_items(item_type, n_items, pdf):
 
 
 @pytest.fixture
-def targets(input_data_items, item_type, operation, metadata):
+def target_data_items(input_data_items, core_operation):
+
+    if core_operation is Nothing:
+        return Nothing
+
+    op = compose(normalize_item, core_operation)
+    expected = lflatten(map(op, input_data_items))
+    return expected
+
+
+@pytest.fixture
+def targets(input_data_items, operation, metadata):
+
     if operation is Nothing:
         return Nothing
+
     op = compose(lift(star(pack)), normalize_item, operation)
     expected = lmap(unpack, flatten(starmap(op, zip(input_data_items, metadata))))
     return expected
diff --git a/test/fixtures/server.py b/test/fixtures/server.py
index dd277be..1e89047 100644
--- a/test/fixtures/server.py
+++ b/test/fixtures/server.py
@@ -72,10 +72,6 @@ def operation(core_operation):
     return op
 
 
-class InvalidParameterCombination(ValueError):
-    pass
-
-
 @pytest.fixture
 def core_operation(item_type, one_to_many):
     def upper(string: bytes):
diff --git a/test/unit_tests/server/pipeline_test.py b/test/unit_tests/server/pipeline_test.py
index 6ba291f..c881b63 100644
--- a/test/unit_tests/server/pipeline_test.py
+++ b/test/unit_tests/server/pipeline_test.py
@@ -12,7 +12,6 @@ from pyinfra.server.receiver.receivers.identity import IdentityReceiver
 from pyinfra.server.receiver.receivers.rest import RestReceiver
 from pyinfra.server.utils import unpack
 from pyinfra.utils.func import lift
-from test.fixtures.server import InvalidParameterCombination
 
 
 def test_mock_pipeline():
@@ -26,16 +25,6 @@ def test_mock_pipeline():
     assert list(pipeline(data)) == list(rcompose(f, g, h, u)(data))
 
 
-def pass_invalid_combination(fn):
-    def inner(*args, **kwargs):
-        try:
-            return fn(*args, **kwargs)
-        except InvalidParameterCombination:
-            pass
-
-    return inner
-
-
 @pytest.mark.parametrize(
     "client_pipeline_type",
     [
diff --git a/test/unit_tests/server/stream_buffer_test.py b/test/unit_tests/server/stream_buffer_test.py
index 2ee429c..662ce3c 100644
--- a/test/unit_tests/server/stream_buffer_test.py
+++ b/test/unit_tests/server/stream_buffer_test.py
@@ -39,6 +39,17 @@ def test_flat_stream_buffer(func, inputs, outputs, buffer_size):
     assert list(flat_stream_buffer([])) == []
 
 
+def test_flat_stream_buffer_on_different_data(core_operation, input_data_items, target_data_items, buffer_size, item_type, one_to_many):
+
+    if core_operation is Nothing:
+        pytest.skip(f"No operation defined for parameter combination: {item_type=}, {one_to_many=}")
+
+    flat_stream_buffer = FlatStreamBuffer(lift(core_operation), buffer_size=buffer_size)
+
+    assert list(flat_stream_buffer(input_data_items)) == target_data_items
+    assert list(flat_stream_buffer([])) == []
+
+
 def test_queued_stream_function(func, inputs, outputs):
     queued_stream_function = QueuedStreamFunction(lift(func))