add test for edf units param

mne/io/edf/edf.py

@@ -147,7 +147,7 @@ def __init__(self, input_fname, eog=None, misc=None, stim_channel='auto',
             units = dict()
 
         for k, (this_ch, this_unit) in enumerate(orig_units.items()):
-            if this_unit != "" and this_unit in units:
+            if this_unit != "" and this_ch in units:
                 raise ValueError(f'Unit for channel {this_ch} is present in '
                                  'the file. Cannot overwrite it with the '
                                  'units argument.')

mne/io/edf/tests/test_edf.py

@@ -77,6 +77,15 @@ def test_orig_units():
     assert orig_units['A1'] == 'µV'  # formerly 'uV' edit by _check_orig_units
 
 
+def test_units_params():
+    """Test enforcing original channel units."""
+
+    with pytest.raises(ValueError,
+                       match=r"Unit for channel .* is present .* Cannot "
+                       "overwrite it"):
+        _ = read_raw_edf(edf_path, units='V', preload=True)
+
+
 def test_subject_info(tmp_path):
     """Test exposure of original channel units."""
     raw = read_raw_edf(edf_path)