improve deprecation warning tests

Author: Yogthos

src/selmer/util.clj

@@ -300,8 +300,8 @@ so it can access vectors as well as maps."
 
 (defonce ^:private warned-keys (atom #{}))
 
-(defn- log-deprecation-warning
-  "Emit a deprecation warning. Tries clojure.tools.logging first, falls back to stderr."
+(defn- default-deprecation-warning-handler
+  "Default handler that tries clojure.tools.logging first, falls back to stderr."
   [message]
   (try
     (require 'clojure.tools.logging)
@@ -315,6 +315,8 @@ so it can access vectors as well as maps."
       (binding [*out* *err*]
         (println "DEPRECATION WARNING:" message)))))
 
+(def ^:dynamic *deprecation-warning-handler* default-deprecation-warning-handler)
+
 (defn deprecated-key-lookup
   "Looks up a key in context-map, preferring the namespaced version (e.g. :selmer/async)
    but falling back to the non-namespaced version (e.g. :async) with a deprecation warning.
@@ -326,7 +328,7 @@ so it can access vectors as well as maps."
       (when (and *warn-on-deprecated-keys*
                  (not (contains? @warned-keys non-namespaced-key)))
         (swap! warned-keys conj non-namespaced-key)
-        (log-deprecation-warning
+        (*deprecation-warning-handler*
           (str "Using " non-namespaced-key " in context is deprecated. "
                "Please use " namespaced-key " instead.")))
       (get context-map non-namespaced-key))))

test/selmer/core_test.clj

@@ -523,30 +523,39 @@
 (deftest script-deprecated-key-warning
   ;; Reset warned-keys so warnings are emitted fresh
   (reset! @#'selmer.util/warned-keys #{})
-  (let [sw (java.io.StringWriter.)]
-    (binding [*err* sw]
+  (let [warnings (atom [])]
+    (binding [*deprecation-warning-handler* #(swap! warnings conj %)]
       (render "{% script \"/js/site.js\" %}" {:async true}))
-    (is (str/includes? (str sw) "DEPRECATION WARNING"))
-    (is (str/includes? (str sw) ":selmer/async")))
+    (is (= 1 (count @warnings)))
+    (is (str/includes? (first @warnings) ":selmer/async")))
   ;; Second call should NOT warn again (once per key per session)
-  (let [sw (java.io.StringWriter.)]
-    (binding [*err* sw]
+  (let [warnings (atom [])]
+    (binding [*deprecation-warning-handler* #(swap! warnings conj %)]
       (render "{% script \"/js/site.js\" %}" {:async true}))
-    (is (= "" (str sw))))
+    (is (= 0 (count @warnings))))
   ;; Reset and test defer warning
   (reset! @#'selmer.util/warned-keys #{})
-  (let [sw (java.io.StringWriter.)]
-    (binding [*err* sw]
+  (let [warnings (atom [])]
+    (binding [*deprecation-warning-handler* #(swap! warnings conj %)]
       (render "{% script \"/js/site.js\" %}" {:defer true}))
-    (is (str/includes? (str sw) "DEPRECATION WARNING"))
-    (is (str/includes? (str sw) ":selmer/defer")))
+    (is (= 1 (count @warnings)))
+    (is (str/includes? (first @warnings) ":selmer/defer")))
   ;; No warning when *warn-on-deprecated-keys* is false
   (reset! @#'selmer.util/warned-keys #{})
-  (let [sw (java.io.StringWriter.)]
-    (binding [*err* sw
+  (let [warnings (atom [])]
+    (binding [*deprecation-warning-handler* #(swap! warnings conj %)
               *warn-on-deprecated-keys* false]
       (render "{% script \"/js/site.js\" %}" {:async true}))
-    (is (= "" (str sw)))))
+    (is (= 0 (count @warnings)))))
+
+(deftest script-deprecated-key-warning-default-handler
+  ;; Verify the default handler writes to stderr (the println fallback path)
+  (reset! @#'selmer.util/warned-keys #{})
+  (let [sw (java.io.StringWriter.)]
+    (binding [*err* sw]
+      (render "{% script \"/js/site.js\" %}" {:async true}))
+    (is (str/includes? (str sw) "DEPRECATION WARNING"))
+    (is (str/includes? (str sw) ":selmer/async"))))
 
 (deftest cycle-test
   (is