diff --git a/lib/iris/tests/unit/common/mixin/test_LimitedAttributeDict.py b/lib/iris/tests/unit/common/mixin/test_LimitedAttributeDict.py
index f538279bb1..4b700aa963 100644
--- a/lib/iris/tests/unit/common/mixin/test_LimitedAttributeDict.py
+++ b/lib/iris/tests/unit/common/mixin/test_LimitedAttributeDict.py
@@ -4,63 +4,55 @@
 # See LICENSE in the root of the repository for full licensing details.
 """Unit tests for the :class:`iris.common.mixin.LimitedAttributeDict`."""
 
-# Import iris.tests first so that some things can be initialised before
-# importing anything else.
-import iris.tests as tests  # isort:skip
-
-from unittest import mock
-
 import numpy as np
+import pytest
 
 from iris.common.mixin import LimitedAttributeDict
 
 
-class Test(tests.IrisTest):
-    def setUp(self):
+class Test:
+    @pytest.fixture(autouse=True)
+    def _setup(self):
         self.forbidden_keys = LimitedAttributeDict.CF_ATTRS_FORBIDDEN
         self.emsg = "{!r} is not a permitted attribute"
 
     def test__invalid_keys(self):
         for key in self.forbidden_keys:
-            with self.assertRaisesRegex(ValueError, self.emsg.format(key)):
+            with pytest.raises(ValueError, match=self.emsg.format(key)):
                 _ = LimitedAttributeDict(**{key: None})
 
-    def test___eq__(self):
+    def test___eq__(self, mocker):
         values = dict(
-            one=mock.sentinel.one,
-            two=mock.sentinel.two,
-            three=mock.sentinel.three,
+            one=mocker.sentinel.one,
+            two=mocker.sentinel.two,
+            three=mocker.sentinel.three,
         )
         left = LimitedAttributeDict(**values)
         right = LimitedAttributeDict(**values)
-        self.assertEqual(left, right)
-        self.assertEqual(left, values)
+        assert left == right
+        assert left == values
 
     def test___eq___numpy(self):
         values = dict(one=np.arange(1), two=np.arange(2), three=np.arange(3))
         left = LimitedAttributeDict(**values)
         right = LimitedAttributeDict(**values)
-        self.assertEqual(left, right)
-        self.assertEqual(left, values)
+        assert left == right
+        assert left == values
         values = dict(one=np.arange(1), two=np.arange(1), three=np.arange(1))
         left = LimitedAttributeDict(dict(one=0, two=0, three=0))
         right = LimitedAttributeDict(**values)
-        self.assertEqual(left, right)
-        self.assertEqual(left, values)
+        assert left == right
+        assert left == values
 
     def test___setitem__(self):
         for key in self.forbidden_keys:
             item = LimitedAttributeDict()
-            with self.assertRaisesRegex(ValueError, self.emsg.format(key)):
+            with pytest.raises(ValueError, match=self.emsg.format(key)):
                 item[key] = None
 
     def test_update(self):
         for key in self.forbidden_keys:
             item = LimitedAttributeDict()
-            with self.assertRaisesRegex(ValueError, self.emsg.format(key)):
-                other = {key: None}
+            other = {key: None}
+            with pytest.raises(ValueError, match=self.emsg.format(key)):
                 item.update(other)
-
-
-if __name__ == "__main__":
-    tests.main()