diff --git a/testing/test_details.py b/testing/test_details.py
index 083f3f05..77fea42f 100644
--- a/testing/test_details.py
+++ b/testing/test_details.py
@@ -124,3 +124,8 @@ def test_result_deprecated():
     r = _Result(10, None)
     with pytest.deprecated_call():
         assert r.result == 10
+
+
+def test_implprefix_deprecated():
+    with pytest.deprecated_call():
+        PluginManager('blah', implprefix='blah')