Raise OptionalImportError when user-specified reader is not installed

monai/transforms/io/array.py

@@ -163,6 +163,10 @@ def __init__(
             expanduser: if True cast filename to Path and call .expanduser on it, otherwise keep filename as is.
             args: additional parameters for reader if providing a reader name.
             kwargs: additional parameters for reader if providing a reader name.
+         Raises:
+            OptionalImportError: If an explicitly selected reader dependency is unavailable.
+
+
 
         Note:
 
@@ -209,10 +213,10 @@ def __init__(
                     the_reader = look_up_option(_r.lower(), SUPPORTED_READERS)
                 try:
                     self.register(the_reader(*args, **kwargs))
-                except OptionalImportError:
-                    warnings.warn(
+                except OptionalImportError as e:
+                    raise OptionalImportError(
                         f"required package for reader {_r} is not installed, or the version doesn't match requirement."
-                    )
+                    ) from e
                 except TypeError:  # the reader doesn't have the corresponding args/kwargs
                     warnings.warn(f"{_r} is not supported with the given parameters {args} {kwargs}.")
                     self.register(the_reader())

tests/transforms/test_load_image.py

@@ -221,9 +221,16 @@ def test_nibabel_reader(self, input_param, filenames, expected_shape):
             assert_allclose(result.affine, torch.eye(4))
             self.assertTupleEqual(result.shape, expected_shape)
 
-    @SkipIfNoModule("nibabel")
-    @SkipIfNoModule("cupy")
-    @SkipIfNoModule("kvikio")
+
+    def test_reader_not_installed_raises(self):
+        from unittest.mock import patch
+        from monai.utils import OptionalImportError
+
+        original_error = OptionalImportError("itk not installed")
+        with patch("monai.data.ITKReader", side_effect=original_error):
+            with self.assertRaises(OptionalImportError) as context:
+                LoadImage(reader="ITKReader")
+        self.assertIs(context.exception.__cause__, original_error)
     @parameterized.expand([TEST_CASE_GPU_1, TEST_CASE_GPU_2, TEST_CASE_GPU_3, TEST_CASE_GPU_4])
     def test_nibabel_reader_gpu(self, input_param, filenames, expected_shape):
         if torch.__version__.endswith("nv24.8"):