add tests and fix handling of immutable case

mne/channels/layout.py

@@ -184,7 +184,7 @@ def pick(self, picks=None, exclude=(), *, verbose=None):
             try:
                 picks = [_ensure_int(picks)]
             except TypeError:
-                picks = list(deepcopy(picks))
+                picks = list(picks) if isinstance(picks, tuple) else deepcopy(picks)
             apply_exclude = False
         if apply_exclude:
             if isinstance(exclude, str):
@@ -193,7 +193,11 @@ def pick(self, picks=None, exclude=(), *, verbose=None):
                 try:
                     exclude = [_ensure_int(exclude)]
                 except TypeError:
-                    exclude = list(deepcopy(exclude))
+                    exclude = (
+                        list(exclude)
+                        if isinstance(exclude, tuple)
+                        else deepcopy(exclude)
+                    )
         for var, var_name in ((picks, "picks"), (exclude, "exclude")):
             if var_name == "exclude" and not apply_exclude:
                 continue
@@ -230,6 +234,12 @@ def pick(self, picks=None, exclude=(), *, verbose=None):
                 )
         if apply_exclude:
             picks = np.array(list(set(picks) - set(exclude)))
+            if len(picks) == 0:
+                raise RuntimeError(
+                    "The channel selection yielded no remaining channels. Please edit "
+                    "the arguments 'picks' and 'exclude' to include at least one "
+                    "channel."
+                )
         else:
             picks = np.array(list(set(picks)))
         self.pos = self.pos[picks]

mne/channels/tests/test_layout.py

@@ -472,4 +472,29 @@ def test_layout_pick_more(layout):
 
 def test_layout_pick_errors(layout):
     """Test validation of layout.pick."""
-    pass
+    with pytest.raises(TypeError, match="must be a list, tuple, set or ndarray"):
+        layout.pick(lambda x: x)
+    with pytest.raises(TypeError, match="must be a list, tuple, set or ndarray"):
+        layout.pick(None, lambda x: x)
+    with pytest.raises(TypeError, match="must be integers or strings"):
+        layout.pick([0, lambda x: x])
+    with pytest.raises(TypeError, match="must be integers or strings"):
+        layout.pick(None, [0, lambda x: x])
+    with pytest.raises(ValueError, match="does not match any channels"):
+        layout.pick("foo")
+    with pytest.raises(ValueError, match="does not match any channels"):
+        layout.pick(None, "foo")
+    with pytest.raises(ValueError, match="does not match any channels"):
+        layout.pick(101)
+    with pytest.raises(ValueError, match="does not match any channels"):
+        layout.pick(None, 101)
+    with pytest.warns(RuntimeWarning, match="has duplicates which will be ignored"):
+        layout.copy().pick(["0", "0"])
+    with pytest.warns(RuntimeWarning, match="has duplicates which will be ignored"):
+        layout.copy().pick(["0", 0])
+    with pytest.warns(RuntimeWarning, match="has duplicates which will be ignored"):
+        layout.copy().pick(None, ["0", "0"])
+    with pytest.warns(RuntimeWarning, match="has duplicates which will be ignored"):
+        layout.copy().pick(None, ["0", 0])
+    with pytest.raises(RuntimeError, match="selection yielded no remaining channels"):
+        layout.copy().pick(None, ["0", "1", "2"])