python
diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
@@ -1225,6 +1225,8 @@ class SubBytes(bytes):
 class ByteArrayTest(BaseBytesTest, unittest.TestCase):
     type2test = bytearray
 
+    _testcapi = import_helper.import_module('_testcapi')
+
     def test_getitem_error(self):
         b = bytearray(b'python')
         msg = "bytearray indices must be integers or slices"
@@ -1317,47 +1319,73 @@ def by(s):
         self.assertEqual(re.findall(br"\w+", b), [by("Hello"), by("world")])
 
     def test_setitem(self):
-        b = bytearray([1, 2, 3])
-        b[1] = 100
-        self.assertEqual(b, bytearray([1, 100, 3]))
-        b[-1] = 200
-        self.assertEqual(b, bytearray([1, 100, 200]))
-        b[0] = Indexable(10)
-        self.assertEqual(b, bytearray([10, 100, 200]))
-        try:
-            b[3] = 0
-            self.fail("Didn't raise IndexError")
-        except IndexError:
-            pass
-        try:
-            b[-10] = 0
-            self.fail("Didn't raise IndexError")
-        except IndexError:
-            pass
-        try:
-            b[0] = 256
-            self.fail("Didn't raise ValueError")
-        except ValueError:
-            pass
-        try:
-            b[0] = Indexable(-1)
-            self.fail("Didn't raise ValueError")
-        except ValueError:
-            pass
-        try:
-            b[0] = None
-            self.fail("Didn't raise TypeError")
-        except TypeError:
-            pass
+        def setitem_as_mapping(b, i, val):
+            b[i] = val
+
+        def setitem_as_sequence(b, i, val):
+            self._testcapi.sequence_setitem(b, i, val)
+
+        def do_tests(setitem):
+            b = bytearray([1, 2, 3])
+            setitem(b, 1, 100)
+            self.assertEqual(b, bytearray([1, 100, 3]))
+            setitem(b, -1, 200)
+            self.assertEqual(b, bytearray([1, 100, 200]))
+            setitem(b, 0, Indexable(10))
+            self.assertEqual(b, bytearray([10, 100, 200]))
+            try:
+                setitem(b, 3, 0)
+                self.fail("Didn't raise IndexError")
+            except IndexError:
+                pass
+            try:
+                setitem(b, -10, 0)
+                self.fail("Didn't raise IndexError")
+            except IndexError:
+                pass
+            try:
+                setitem(b, 0, 256)
+                self.fail("Didn't raise ValueError")
+            except ValueError:
+                pass
+            try:
+                setitem(b, 0, Indexable(-1))
+                self.fail("Didn't raise ValueError")
+            except ValueError:
+                pass
+            try:
+                setitem(b, 0, None)
+                self.fail("Didn't raise TypeError")
+            except TypeError:
+                pass
+
+        with self.subTest("tp_as_mapping"):
+            do_tests(setitem_as_mapping)
+
+        with self.subTest("tp_as_sequence"):
+            do_tests(setitem_as_sequence)
 
     def test_delitem(self):
-        b = bytearray(range(10))
-        del b[0]
-        self.assertEqual(b, bytearray(range(1, 10)))
-        del b[-1]
-        self.assertEqual(b, bytearray(range(1, 9)))
-        del b[4]
-        self.assertEqual(b, bytearray([1, 2, 3, 4, 6, 7, 8]))
+        def del_as_mapping(b, i):
+            del b[i]
+
+        def del_as_sequence(b, i):
+            self._testcapi.sequence_delitem(b, i)
+
+        def do_tests(delete):
+            b = bytearray(range(10))
+            delete(b, 0)
+            self.assertEqual(b, bytearray(range(1, 10)))
+            delete(b, -1)
+            self.assertEqual(b, bytearray(range(1, 9)))
+            delete(b, 4)
+            self.assertEqual(b, bytearray([1, 2, 3, 4, 6, 7, 8]))
+
+        with self.subTest("tp_as_mapping"):
+            do_tests(del_as_mapping)
+
+        with self.subTest("tp_as_sequence"):
+            do_tests(del_as_sequence)
 
     def test_setslice(self):
         b = bytearray(range(10))
@@ -1729,6 +1757,8 @@ def test_repeat_after_setslice(self):
         self.assertEqual(b3, b'xcxcxc')
 
     def test_mutating_index(self):
+        # See gh-91153
+
         class Boom:
             def __index__(self):
                 b.clear()
@@ -1740,10 +1770,9 @@ def __index__(self):
                 b[0] = Boom()
 
         with self.subTest("tp_as_sequence"):
-            _testcapi = import_helper.import_module('_testcapi')
             b = bytearray(b'Now you see me...')
             with self.assertRaises(IndexError):
-                _testcapi.sequence_setitem(b, 0, Boom())
+                self._testcapi.sequence_setitem(b, 0, Boom())
 
 
 class AssortedBytesTest(unittest.TestCase):

diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
@@ -4846,6 +4846,20 @@ sequence_setitem(PyObject *self, PyObject *args)
 }
 
 
+static PyObject *
+sequence_delitem(PyObject *self, PyObject *args)
+{
+    Py_ssize_t i;
+    PyObject *seq;
+    if (!PyArg_ParseTuple(args, "On", &seq, &i)) {
+        return NULL;
+    }
+    if (PySequence_DelItem(seq, i)) {
+        return NULL;
+    }
+    Py_RETURN_NONE;
+}
+
 static PyObject *
 hasattr_string(PyObject *self, PyObject* args)
 {
@@ -5732,6 +5746,7 @@ static PyMethodDef TestMethods[] = {
     {"write_unraisable_exc", test_write_unraisable_exc, METH_VARARGS},
     {"sequence_getitem", sequence_getitem, METH_VARARGS},
     {"sequence_setitem", sequence_setitem, METH_VARARGS},
+    {"sequence_delitem", sequence_delitem, METH_VARARGS},
     {"hasattr_string", hasattr_string, METH_VARARGS},
     {"meth_varargs", meth_varargs, METH_VARARGS},
     {"meth_varargs_keywords", _PyCFunction_CAST(meth_varargs_keywords), METH_VARARGS|METH_KEYWORDS},