TEST: Mark large data file test as xfail

Author: effigies

nibabel/nicom/tests/test_dicomwrappers.py

@@ -628,6 +628,7 @@ def test_affine(self):
         aff = dw.affine
 
     @dicom_test
+    @pytest.mark.xfail(reason='Not packaged in install', raises=FileNotFoundError)
     def test_data_real(self):
         # The data in this file is (initially) a 1D gradient so it compresses
         # well.  This just tests that the data ordering produces a consistent