diff --git a/news/xtype.rst b/news/xtype.rst
new file mode 100644
index 00000000..24a78758
--- /dev/null
+++ b/news/xtype.rst
@@ -0,0 +1,23 @@
+**Added:**
+
+* functionality to return the 2D array based on the specified xtype
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>
diff --git a/src/diffpy/utils/diffraction_objects.py b/src/diffpy/utils/diffraction_objects.py
index 54374fa7..703baf03 100644
--- a/src/diffpy/utils/diffraction_objects.py
+++ b/src/diffpy/utils/diffraction_objects.py
@@ -21,7 +21,7 @@
 
 def _xtype_wmsg(xtype):
     return (
-        f"WARNING: I don't know how to handle the xtype, '{xtype}'.  Please rerun specifying an "
+        f"I don't know how to handle the xtype, '{xtype}'. Please rerun specifying an "
         f"xtype from {*XQUANTITIES, }"
     )
 
@@ -376,16 +376,17 @@ def scale_to(self, target_diff_object, xtype=None, xvalue=None):
         return scaled
 
     def on_xtype(self, xtype):
-        """
-        return a 2D np array with x in the first column and y in the second for x of type type
+        f"""
+        return a list of two 1D np array with x and y data, raise an error if the specified xtype is invalid
 
         Parameters
         ----------
-        xtype
+        xtype str
+            the type of quantity for the independent variable from {*XQUANTITIES, }
 
         Returns
         -------
-
+        a list of two 1D np array with x and y data
         """
         if xtype.lower() in ANGLEQUANTITIES:
             return self.on_tth()
@@ -394,7 +395,7 @@ def on_xtype(self, xtype):
         elif xtype.lower() in DQUANTITIES:
             return self.on_d()
         else:
-            warnings.warn(_xtype_wmsg(xtype))
+            raise ValueError(_xtype_wmsg(xtype))
 
     def dump(self, filepath, xtype=None):
         if xtype is None:
diff --git a/tests/test_diffraction_objects.py b/tests/test_diffraction_objects.py
index 9db6932e..2371838f 100644
--- a/tests/test_diffraction_objects.py
+++ b/tests/test_diffraction_objects.py
@@ -1,11 +1,11 @@
+import re
 from pathlib import Path
 
 import numpy as np
 import pytest
 from freezegun import freeze_time
 
-from diffpy.utils.diffraction_objects import DiffractionObject
-from diffpy.utils.transforms import wavelength_warning_emsg
+from diffpy.utils.diffraction_objects import XQUANTITIES, DiffractionObject
 
 
 def compare_dicts(dict1, dict2):
@@ -202,13 +202,24 @@ def test_diffraction_objects_equality(inputs1, inputs2, expected):
     assert dicts_equal(diffraction_object1.__dict__, diffraction_object2.__dict__) == expected
 
 
-def _test_valid_diffraction_objects(actual_diffraction_object, function, expected_array):
-    if actual_diffraction_object.wavelength is None:
-        with pytest.warns(UserWarning) as warn_record:
-            getattr(actual_diffraction_object, function)()
-        assert str(warn_record[0].message) == wavelength_warning_emsg
-    actual_array = getattr(actual_diffraction_object, function)()
-    return np.allclose(actual_array, expected_array)
+def test_on_xtype():
+    test = DiffractionObject(wavelength=2 * np.pi, xarray=np.array([30, 60]), yarray=np.array([1, 2]), xtype="tth")
+    assert np.allclose(test.on_xtype("tth"), [np.array([30, 60]), np.array([1, 2])])
+    assert np.allclose(test.on_xtype("2theta"), [np.array([30, 60]), np.array([1, 2])])
+    assert np.allclose(test.on_xtype("q"), [np.array([0.51764, 1]), np.array([1, 2])])
+    assert np.allclose(test.on_xtype("d"), [np.array([12.13818, 6.28319]), np.array([1, 2])])
+
+
+def test_on_xtype_bad():
+    test = DiffractionObject()
+    with pytest.raises(
+        ValueError,
+        match=re.escape(
+            f"I don't know how to handle the xtype, 'invalid'. Please rerun specifying an "
+            f"xtype from {*XQUANTITIES, }"
+        ),
+    ):
+        test.on_xtype("invalid")
 
 
 def test_dump(tmp_path, mocker):