test: add iOS playback observer lifecycle regression

Author: moonggae

shared/src/iosTest/kotlin/io/github/moonggae/kmedia/session/PlaybackStateObserverManagerTest.kt

@@ -0,0 +1,32 @@
+package io.github.moonggae.kmedia.session
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.cancel
+import platform.AVFoundation.AVPlayer
+import kotlin.test.Test
+
+class PlaybackStateObserverManagerTest {
+    @Test
+    fun observingLifecycleIsIdempotentAcrossRestart() {
+        val scope = CoroutineScope(SupervisorJob() + Dispatchers.Default)
+        val manager = PlaybackStateObserverManager(
+            player = AVPlayer(),
+            coroutineScope = scope,
+            onPlaybackStateChanged = {}
+        )
+
+        try {
+            manager.stopObserving()
+            manager.startObserving()
+            manager.startObserving()
+            manager.stopObserving()
+            manager.stopObserving()
+            manager.startObserving()
+            manager.stopObserving()
+        } finally {
+            scope.cancel()
+        }
+    }
+}