Fix playback stopping when fallback audio ends

frontend/test/arthur/audio/mix_test.cljs

@@ -0,0 +1,25 @@
+(ns arthur.audio.mix-test
+  (:require [arthur.audio.mix :as mix]
+            [cljs.test :refer [deftest is]]))
+
+(defn- buffer [samples]
+  (let [data (js/Float32Array. (clj->js samples))]
+    #js {:sampleRate 12 :length (count samples) :numberOfChannels 1
+         :getChannelData (fn [_] data)}))
+
+(deftest fallback-audio-follows-the-timeline-length
+  (let [original (.-OfflineAudioContext js/globalThis)]
+    (set! (.-OfflineAudioContext js/globalThis)
+          (fn [_ _ _]
+            #js {:createBuffer (fn [_ frames _] (buffer (repeat frames 0)))}))
+    (try
+      (let [short (buffer (repeat 92 0.5))
+            fitted (mix/fit-buffer short (/ 5008 12))
+            data (.getChannelData fitted 0)]
+        (is (= 5008 (.-length fitted)))
+        (is (= 0.5 (aget data 91)))
+        (is (= 0 (aget data 92)))
+        (is (= 0 (aget data 5007)))
+        (is (identical? short (mix/fit-buffer short (/ 92 12))))
+        (is (= 20 (.-length (mix/fit-buffer short (/ 20 12))))))
+      (finally (set! (.-OfflineAudioContext js/globalThis) original)))))