Improve msd_type error handling

Author: tani-dubey

package/MDAnalysis/analysis/msd.py

@@ -385,8 +385,8 @@ def _parse_msd_type(self):
         try:
             self._dim = keys[self.msd_type.lower()]
         except (AttributeError, KeyError):
-            raise TypeError(
-                "msd_type must be a string and one of: xyz, xy, xz, yz, x, y, z"
+            raise ValueError(
+                f"Invalid msd_type {self.msd_type.lower()} must be a string and one of: xyz, xy, xz, yz, x, y, z"
             )
 
         self.dim_fac = len(self._dim)

testsuite/MDAnalysisTests/analysis/test_msd.py

@@ -118,20 +118,12 @@ def test_updating_ag_rejected(self, u):
             m = MSD(updating_ag, msd_type="xyz", fft=False)
 
     @pytest.mark.parametrize(
-        "msd_type, exc",
-        [
-            ("Xz", None),  # valid, mixed case.
-            (123, TypeError),  # non-string.
-        ],
+        "msdtype", ["foo", "bar", "yx", "zyx", 123, "", " xy "]
     )
-    def test_msdtype_error(self, u, SELECTION, msd_type, exc):
-        if exc is None:
-            m = MSD(u, SELECTION, msd_type=msd_type, fft=False)
-            assert m.dim_fac == 2
-            assert m._dim == [0, 2]
-        else:
-            with pytest.raises(exc):
-                MSD(u, SELECTION, msd_type=msd_type, fft=False)
+    def test_msdtype_error(self, u, SELECTION, msdtype):
+        errmsg = f"invalid msd_type: {msdtype}"
+        with pytest.raises(ValueError, match=errmsg):
+            m = MSD(u, SELECTION, msd_type=msdtype)
 
     @pytest.mark.parametrize(
         "dim, dim_factor",