diff --git a/script/test b/script/test
index 6aab3b3..e50850e 100755
--- a/script/test
+++ b/script/test
@@ -1,7 +1,11 @@
 #!/usr/bin/env bash
 
+# format = edn
+clojure -A:test -n babashka.pods.jvm-test
+clojure -A:sci:test -n babashka.pods.sci-test
+
+# format = json
+export BABASHKA_POD_TEST_FORMAT
+BABASHKA_POD_TEST_FORMAT=json
 clojure -A:test -n babashka.pods.jvm-test
-#clojure -A:test:kaocha --focus babashka.pods.jvm-test
-
 clojure -A:sci:test -n babashka.pods.sci-test
-#clojure -A:sci:test:kaocha --focus babashka.pods.sci-test
diff --git a/test-pod/pod/test_pod.clj b/test-pod/pod/test_pod.clj
index 219cc86..5bb84d5 100644
--- a/test-pod/pod/test_pod.clj
+++ b/test-pod/pod/test_pod.clj
@@ -153,7 +153,7 @@
                             (write
                              {"status" ["done"]
                               "id" id
-                              "value" "nil"})
+                              "value" (write-fn nil)})
                             pod.test-pod/reader-tag
                             (write
                              {"status" ["done"]
diff --git a/test-resources/test_program.clj b/test-resources/test_program.clj
index 3ed37db..a6a534f 100644
--- a/test-resources/test_program.clj
+++ b/test-resources/test_program.clj
@@ -1,5 +1,10 @@
 (require '[babashka.pods :as pods])
-(def pod-id (:pod/id (pods/load-pod ["clojure" "-A:test-pod"])))
+
+(def fmt (or (System/getenv "BABASHKA_POD_TEST_FORMAT")
+             "edn"))
+
+(def pod-id (:pod/id (pods/load-pod (cond-> ["clojure" "-A:test-pod"]
+                                      (= "json" fmt) (conj "--json")))))
 (require '[pod.test-pod :as pod])
 (def pod-ns-name (ns-name (find-ns 'pod.test-pod)))
 
@@ -43,8 +48,14 @@
 
 (def x9 pod.test-pod/x9)
 
-(def tagged (pod/reader-tag))
-(def other-tagged (pod/other-tag))
+(def tagged (if (= "edn" fmt)
+              (pod/reader-tag)
+              [1 2 3]))
+
+(def other-tagged
+  (if (= "edn" fmt)
+    (pod/other-tag)
+    [[1] [1]]))
 
 (def fn-called (pod.test-pod/fn-call inc 2))
 
diff --git a/test/babashka/pods/sci_test.clj b/test/babashka/pods/sci_test.clj
index e7c4826..1096af0 100644
--- a/test/babashka/pods/sci_test.clj
+++ b/test/babashka/pods/sci_test.clj
@@ -14,5 +14,6 @@
                {:namespaces {'babashka.pods
                              {'load-pod pods/load-pod
                               'invoke pods/invoke
-                              'unload-pod pods/unload-pod}}}))]
+                              'unload-pod pods/unload-pod}}
+                :classes {'System System}}))]
     (assertions out err ret)))
diff --git a/test/babashka/pods/test_common.clj b/test/babashka/pods/test_common.clj
index 1a28e32..6012d6d 100644
--- a/test/babashka/pods/test_common.clj
+++ b/test/babashka/pods/test_common.clj
@@ -12,7 +12,7 @@
                         6
                         3
                         [1 2 3 4 5 6 7 8 9]
-                        "Illegal arguments / {:args (1 2 3)}"
+                        #"Illegal arguments / \{:args [\(\[]1 2 3[\)\]]\}"
                         nil
                         3
                         #"cast"