diff --git a/services/analysis-engine/tests/test_api.py b/services/analysis-engine/tests/test_api.py
index ea55cba2..029cb087 100644
--- a/services/analysis-engine/tests/test_api.py
+++ b/services/analysis-engine/tests/test_api.py
@@ -926,9 +926,7 @@ def put(self, item: tuple[str, object]) -> None:
         assert archive["stem_bass"].shape == (4,)
 
 
-def test_stem_separation_process_helper_maps_worker_results(tmp_path) -> None:
-    """Ensure parent-side process helper maps worker result envelopes."""
-
+def _make_fake_multiprocessing_context(item: tuple[str, object]) -> object:
     class FakeQueue:
         def __init__(self, item: tuple[str, object]) -> None:
             self.item = item
@@ -965,12 +963,20 @@ def Queue(self, maxsize: int) -> FakeQueue:
             assert maxsize == 1
             return FakeQueue(self.item)
 
+    return FakeContext(item)
+
+
+def test_stem_separation_process_helper_maps_ok_envelope() -> None:
+    """Ensure parent-side process helper maps ok worker result envelopes."""
     with patch(
         "bandscope_analysis.api._multiprocessing_context",
-        return_value=FakeContext(("ok", {"stems": {}})),
+        return_value=_make_fake_multiprocessing_context(("ok", {"stems": {}})),
     ):
         assert _run_stem_separation_with_timeout("/tmp/audio.wav") == {"stems": {}}
 
+
+def test_stem_separation_process_helper_maps_ok_file_envelope(tmp_path) -> None:
+    """Ensure parent-side process helper maps ok_file worker result envelopes."""
     arrays_path = tmp_path / "worker-stems.npz"
     np.savez_compressed(arrays_path, stem_bass=np.ones(4))
     file_payload = {
@@ -982,7 +988,7 @@ def Queue(self, maxsize: int) -> FakeQueue:
     }
     with patch(
         "bandscope_analysis.api._multiprocessing_context",
-        return_value=FakeContext(("ok_file", file_payload)),
+        return_value=_make_fake_multiprocessing_context(("ok_file", file_payload)),
     ):
         loaded = _run_stem_separation_with_timeout("/tmp/audio.wav")
     assert loaded["sr"] == 22050
@@ -990,6 +996,9 @@ def Queue(self, maxsize: int) -> FakeQueue:
     assert loaded["stem_role_types"] == {"bass": "instrument"}
     assert not arrays_path.with_suffix(".json").exists()
 
+
+def test_stem_separation_process_helper_rejects_invalid_file_payloads(tmp_path) -> None:
+    """Ensure parent-side process helper rejects invalid ok_file payloads."""
     invalid_file_payloads = [
         ("not-a-dict", "Stem separation returned invalid metadata."),
         (
@@ -1016,7 +1025,7 @@ def Queue(self, maxsize: int) -> FakeQueue:
     for payload, expected_message in invalid_file_payloads:
         with patch(
             "bandscope_analysis.api._multiprocessing_context",
-            return_value=FakeContext(("ok_file", payload)),
+            return_value=_make_fake_multiprocessing_context(("ok_file", payload)),
         ):
             try:
                 _run_stem_separation_with_timeout("/tmp/audio.wav")
@@ -1025,6 +1034,9 @@ def Queue(self, maxsize: int) -> FakeQueue:
             else:
                 raise AssertionError("Expected RuntimeError")
 
+
+def test_stem_separation_process_helper_maps_error_envelopes() -> None:
+    """Ensure parent-side process helper maps error envelopes to exceptions."""
     error_cases = [
         (("file_not_found", "missing"), FileNotFoundError),
         (("value_error", "bad media"), ValueError),
@@ -1033,7 +1045,7 @@ def Queue(self, maxsize: int) -> FakeQueue:
     for item, expected_error in error_cases:
         with patch(
             "bandscope_analysis.api._multiprocessing_context",
-            return_value=FakeContext(item),
+            return_value=_make_fake_multiprocessing_context(item),
         ):
             try:
                 _run_stem_separation_with_timeout("/tmp/audio.wav")