diff --git a/keymapper/X.py b/keymapper/X.py
index 4dbe4f32..c9932cab 100644
--- a/keymapper/X.py
+++ b/keymapper/X.py
@@ -91,10 +91,11 @@ class Mapping:
         Parameters
         ----------
         previous_keycode : int or None
+            If None, will not remove any previous mapping.
         new_keycode : int
         character : string
         """
-        if new_keycode and character and new_keycode != previous_keycode:
+        if new_keycode and character:
             self._mapping[new_keycode] = character
             if new_keycode != previous_keycode:
                 # clear previous mapping of that code, because the line
@@ -113,21 +114,6 @@ class Mapping:
         if self._mapping.get(keycode) is not None:
             del self._mapping[keycode]
 
-    def add(self, keycode, character):
-        """Add a mapping for a hardware key to a character.
-
-        Parameters
-        ----------
-        keycode : int
-        character : string
-        """
-        if self._mapping.get(keycode) is not None:
-            raise KeyError(
-                f'Keycode {keycode} is already mapped '
-                f'to {self._mapping.get(keycode)}'
-            )
-        self._mapping[keycode] = character
-
     def get(self, keycode):
         """Read the character that is mapped to this keycode.
 
diff --git a/tests/testcases/X.py b/tests/testcases/X.py
index e9426266..f9ddc688 100644
--- a/tests/testcases/X.py
+++ b/tests/testcases/X.py
@@ -21,10 +21,50 @@
 
 import unittest
 
+from keymapper.X import Mapping
 
-class TestX(unittest.TestCase):
-    # TODO test the mapping object
-    pass
+
+class TestMapping(unittest.TestCase):
+    def setUp(self):
+        self.mapping = Mapping()
+
+    def test_change(self):
+        # 1 is not assigned yet, just add it
+        self.mapping.change(1, 2, 'a')
+        self.assertIsNone(self.mapping.get(1))
+        self.assertEqual(self.mapping.get(2), 'a')
+        self.assertEqual(len(self.mapping), 1)
+
+        # change 2 to 3 and change a to b
+        self.mapping.change(2, 3, 'b')
+        self.assertIsNone(self.mapping.get(2))
+        self.assertEqual(self.mapping.get(3), 'b')
+        self.assertEqual(len(self.mapping), 1)
+
+        # add 4
+        self.mapping.change(None, 4, 'c')
+        self.assertEqual(self.mapping.get(3), 'b')
+        self.assertEqual(self.mapping.get(4), 'c')
+        self.assertEqual(len(self.mapping), 2)
+
+        # change the mapping of 4 to d
+        self.mapping.change(None, 4, 'd')
+        self.assertEqual(self.mapping.get(4), 'd')
+        self.assertEqual(len(self.mapping), 2)
+
+        # this also works in the same way
+        self.mapping.change(4, 4, 'e')
+        self.assertEqual(self.mapping.get(4), 'e')
+        self.assertEqual(len(self.mapping), 2)
+
+    def test_clear(self):
+        self.mapping.change(None, 10, 'NUM1')
+        self.mapping.change(None, 20, 'NUM2')
+        self.mapping.change(None, 30, 'NUM3')
+        self.mapping.clear(20)
+        self.assertEqual(self.mapping.get(10), 'NUM1')
+        self.assertIsNone(self.mapping.get(20))
+        self.assertEqual(self.mapping.get(30), 'NUM3')
 
 
 if __name__ == "__main__":