diff --git a/test/cider/nrepl/middleware/undef_test.clj b/test/cider/nrepl/middleware/undef_test.clj
index 5b65a1e8c..0c303cfb2 100644
--- a/test/cider/nrepl/middleware/undef_test.clj
+++ b/test/cider/nrepl/middleware/undef_test.clj
@@ -1,14 +1,60 @@
 (ns cider.nrepl.middleware.undef-test
-  (:require
-   [clojure.test :refer :all]
-   [cider.nrepl.middleware.test-transport :refer [messages test-transport]]
-   [cider.nrepl.middleware.undef :refer [undef-reply]]))
-
-(def x 1)
-
-(deftest test-toogle-undef-op
-  (let [transport (test-transport)]
-    (is (ns-resolve 'cider.nrepl.middleware.undef-test 'x))
-    (undef-reply {:transport transport :ns "cider.nrepl.middleware.undef-test" :symbol "x"})
-    (is (= [{:status #{:done}}] (messages transport)))
-    (is (nil? (ns-resolve 'cider.nrepl.middleware.undef-test 'x)))))
+  (:require [cider.nrepl.middleware.test-session :as session]
+            [clojure.test :refer :all]))
+
+(use-fixtures :each session/session-fixture)
+
+(deftest undef-var
+  (testing "undef undefines vars"
+    (is (= ["#'user/x"]
+           (:value (session/message {:op "eval"
+                                     :code "(def x 1)"}))))
+    (is (= ["#'user/x"]
+           (:value (session/message {:op "eval"
+                                     :code "(ns-resolve 'user 'x)"}))))
+    (is (= #{"done"}
+           (:status (session/message {:op "undef"
+                                      :ns "user"
+                                      :symbol "x"}))))
+    (is (= ["nil"]
+           (:value (session/message {:op "eval"
+                                     :code "(ns-resolve 'user 'x)"}))))))
+
+(deftest undef-alias
+  (testing "undef undefines aliases"
+    (is (= ["#'clojure.walk/postwalk"]
+           (:value (do
+                     (session/message {:op "eval"
+                                       :code "(require '[clojure.walk :refer [postwalk]])"})
+                     (session/message {:op "eval"
+                                       :code "(ns-resolve 'user 'postwalk)"})))))
+    (is (= #{"done"}
+           (:status (session/message {:op "undef"
+                                      :ns "user"
+                                      :symbol "postwalk"}))))
+    (is (= ["nil"]
+           (:value (session/message {:op "eval"
+                                     :code "(ns-resolve 'user 'postwalk)"}))))))
+
+(deftest undef-undefined
+  (testing "undef does not throw for aliases or vars that are not defined"
+    (is (= ["nil"]
+           (:value (session/message {:op "eval"
+                                     :code "(ns-resolve 'user 'x)"}))))
+    (is (= #{"done"}
+           (:status (session/message {:op "undef"
+                                      :ns "user"
+                                      :symbol "x"}))))))
+
+(deftest undef-exceptions
+  (testing "undef throws for non-existent namespaces"
+    (is (= #{"done" "undef-error"}
+           (:status (session/message {:op "undef"
+                                      :ns "abc"
+                                      :symbol "x"})))))
+
+  (testing "undef throws with missing arguments"
+    (is (= #{"done" "undef-error"}
+           (:status (session/message {:op "undef"}))
+           (:status (session/message {:op "undef" :ns "user"}))
+           (:status (session/message {:op "undef" :symbol "x"}))))))