Test missing-path validation API and document discovery timing

dandi/files/__init__.py

@@ -85,9 +85,14 @@ def find_dandi_files(
     they are of a type represented by a `LocalDirectoryAsset` subclass, in
     which case they are not recursed into.
 
-    All requested paths are checked before any files are yielded.  A missing
-    path raises `FileNotFoundError`; a broken symlink is still discovered so
-    that the caller can apply its missing-content policy.
+    All requested paths are checked before any files are yielded.  Because this
+    function is a generator, a missing path raises `FileNotFoundError` when
+    the iterator is first advanced, not when the function is called.  A broken
+    symlink is still discovered so that the caller can apply its
+    missing-content policy.
+
+    .. versionchanged:: 0.82.0
+        Missing requested paths now raise `FileNotFoundError` on iteration.
 
     :param dandiset_path:
         The path to the root of the Dandiset in which the paths are located.

dandi/validate/tests/test_core.py

@@ -55,6 +55,18 @@ def test_validate_empty(tmp_path: Path) -> None:
     ]
 
 
+@pytest.mark.ai_generated
+@pytest.mark.parametrize("use_path", [False, True])
+def test_validate_missing_path(tmp_path: Path, use_path: bool) -> None:
+    (tmp_path / dandiset_metadata_file).write_text("identifier: 123456\n")
+    missing = tmp_path / "missing.nwb"
+    requested_path = missing if use_path else str(missing)
+
+    with pytest.raises(FileNotFoundError) as exc:
+        list(validate(requested_path))
+    assert exc.value.filename == str(missing)
+
+
 def test_validate_just_dandiset_yaml(tmp_path: Path) -> None:
     (tmp_path / dandiset_metadata_file).write_text(
         "identifier: 12346\nname: Foo\ndescription: Dandiset Foo\n"