ENH: give informative assertion message when multiple values are found

heudiconv/heuristics/reproin.py

@@ -637,12 +637,14 @@ def from_series_info(name: str) -> Optional[str]:
         # For scouts -- we want only dicoms
         # https://github.com/nipy/heudiconv/issues/145
         outtype: tuple[str, ...]
-        if "_Scout" in s.series_description or (
-            datatype == "anat"
-            and datatype_suffix
-            and datatype_suffix.startswith("scout")
-        ) or (
-            s.series_description.lower() == s.protocol_name.lower() + "_setter"
+        if (
+            "_Scout" in s.series_description
+            or (
+                datatype == "anat"
+                and datatype_suffix
+                and datatype_suffix.startswith("scout")
+            )
+            or (s.series_description.lower() == s.protocol_name.lower() + "_setter")
         ):
             outtype = ("dicom",)
         else:
@@ -725,7 +727,11 @@ def get_unique(seqinfos: list[SeqInfo], attr: str) -> Any:
 
     """
     values = set(getattr(si, attr) for si in seqinfos)
-    assert len(values) == 1
+    if len(values) != 1:
+        raise AssertionError(
+            f"Was expecting a single value for attribute {attr!r} "
+            f"but got: {', '.join(sorted(values))}"
+        )
     return values.pop()
 
 

heudiconv/heuristics/test_reproin.py

@@ -7,19 +7,29 @@
 from typing import NamedTuple
 from unittest.mock import patch
 
+import pytest
+
 from . import reproin
 from .reproin import (
     filter_files,
     fix_canceled_runs,
     fix_dbic_protocol,
     fixup_subjectid,
     get_dups_marked,
+    get_unique,
     md5sum,
     parse_series_spec,
     sanitize_str,
 )
 
 
+class FakeSeqInfo(NamedTuple):
+    accession_number: str
+    study_description: str
+    field1: str
+    field2: str
+
+
 def test_get_dups_marked() -> None:
     no_dups: dict[tuple[str, tuple[str, ...], None], list[int]] = {
         ("some", ("foo",), None): [1]
@@ -97,12 +107,6 @@ class FakeSeqInfo(NamedTuple):
 
 
 def test_fix_dbic_protocol() -> None:
-    class FakeSeqInfo(NamedTuple):
-        accession_number: str
-        study_description: str
-        field1: str
-        field2: str
-
     accession_number = "A003"
     seq1 = FakeSeqInfo(
         accession_number,
@@ -235,3 +239,19 @@ def test_parse_series_spec() -> None:
         "session": "01",
         "dir": "AP",
     }
+
+
+def test_get_unique() -> None:
+    accession_number = "A003"
+    acqs = [
+        FakeSeqInfo(accession_number, "mystudy", "nochangeplease", "nochangeeither"),
+        FakeSeqInfo(accession_number, "mystudy2", "nochangeplease", "nochangeeither"),
+    ]
+
+    assert get_unique(acqs, "accession_number") == accession_number  # type: ignore[arg-type]
+    with pytest.raises(AssertionError) as ce:
+        get_unique(acqs, "study_description")  # type: ignore[arg-type]
+    assert (
+        str(ce.value)
+        == "Was expecting a single value for attribute 'study_description' but got: mystudy, mystudy2"
+    )