diff --git a/app/src/test/java/xyz/cottongin/radio247/service/PlaybackStateMachineTest.kt b/app/src/test/java/xyz/cottongin/radio247/service/PlaybackStateMachineTest.kt
new file mode 100644
index 0000000..c358d4a
--- /dev/null
+++ b/app/src/test/java/xyz/cottongin/radio247/service/PlaybackStateMachineTest.kt
@@ -0,0 +1,163 @@
+package xyz.cottongin.radio247.service
+
+import kotlinx.coroutines.flow.MutableStateFlow
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+import xyz.cottongin.radio247.data.model.Station
+
+class PlaybackStateMachineTest {
+
+    private lateinit var stateFlow: MutableStateFlow<PlaybackState>
+    private val testStation = Station(
+        id = 1L,
+        name = "Test Station",
+        url = "http://example.com/stream"
+    )
+    private val testUrls = listOf(
+        "http://example.com/stream1",
+        "http://example.com/stream2"
+    )
+
+    @Before
+    fun setUp() {
+        stateFlow = MutableStateFlow(PlaybackState.Idle)
+    }
+
+    @Test
+    fun `idle to connecting on play`() {
+        val newState = PlaybackState.Connecting(
+            station = testStation,
+            urls = testUrls,
+            currentUrlIndex = 0
+        )
+        stateFlow.value = newState
+        assertTrue(stateFlow.value is PlaybackState.Connecting)
+        assertEquals(0, (stateFlow.value as PlaybackState.Connecting).currentUrlIndex)
+    }
+
+    @Test
+    fun `connecting to playing on engine started`() {
+        stateFlow.value = PlaybackState.Connecting(station = testStation, urls = testUrls)
+        val connectionStartedAt = System.currentTimeMillis()
+        stateFlow.value = PlaybackState.Playing(
+            station = testStation,
+            sessionStartedAt = connectionStartedAt,
+            connectionStartedAt = connectionStartedAt
+        )
+        assertTrue(stateFlow.value is PlaybackState.Playing)
+    }
+
+    @Test
+    fun `connecting advances URL index on connection failure`() {
+        stateFlow.value = PlaybackState.Connecting(
+            station = testStation, urls = testUrls, currentUrlIndex = 0
+        )
+        stateFlow.value = PlaybackState.Connecting(
+            station = testStation, urls = testUrls, currentUrlIndex = 1
+        )
+        assertEquals(1, (stateFlow.value as PlaybackState.Connecting).currentUrlIndex)
+    }
+
+    @Test
+    fun `connecting to reconnecting when all URLs exhausted and stayConnected`() {
+        stateFlow.value = PlaybackState.Connecting(
+            station = testStation, urls = testUrls, currentUrlIndex = 1
+        )
+        stateFlow.value = PlaybackState.Reconnecting(
+            station = testStation, attempt = 1, sessionStartedAt = 0L
+        )
+        assertTrue(stateFlow.value is PlaybackState.Reconnecting)
+    }
+
+    @Test
+    fun `connecting to idle when all URLs exhausted and not stayConnected`() {
+        stateFlow.value = PlaybackState.Connecting(
+            station = testStation, urls = testUrls, currentUrlIndex = 1
+        )
+        stateFlow.value = PlaybackState.Idle
+        assertTrue(stateFlow.value is PlaybackState.Idle)
+    }
+
+    @Test
+    fun `playing to paused on user pause`() {
+        val now = System.currentTimeMillis()
+        stateFlow.value = PlaybackState.Playing(
+            station = testStation, sessionStartedAt = now, connectionStartedAt = now
+        )
+        stateFlow.value = PlaybackState.Paused(
+            station = testStation, sessionStartedAt = now
+        )
+        assertTrue(stateFlow.value is PlaybackState.Paused)
+    }
+
+    @Test
+    fun `playing to reconnecting on connection lost with stayConnected`() {
+        val now = System.currentTimeMillis()
+        stateFlow.value = PlaybackState.Playing(
+            station = testStation, sessionStartedAt = now, connectionStartedAt = now
+        )
+        stateFlow.value = PlaybackState.Reconnecting(
+            station = testStation, sessionStartedAt = now, attempt = 1
+        )
+        assertTrue(stateFlow.value is PlaybackState.Reconnecting)
+    }
+
+    @Test
+    fun `playing to idle on connection lost without stayConnected`() {
+        val now = System.currentTimeMillis()
+        stateFlow.value = PlaybackState.Playing(
+            station = testStation, sessionStartedAt = now, connectionStartedAt = now
+        )
+        stateFlow.value = PlaybackState.Idle
+        assertTrue(stateFlow.value is PlaybackState.Idle)
+    }
+
+    @Test
+    fun `paused to connecting on resume`() {
+        val now = System.currentTimeMillis()
+        stateFlow.value = PlaybackState.Paused(
+            station = testStation, sessionStartedAt = now
+        )
+        stateFlow.value = PlaybackState.Connecting(
+            station = testStation, urls = testUrls, currentUrlIndex = 0
+        )
+        assertTrue(stateFlow.value is PlaybackState.Connecting)
+    }
+
+    @Test
+    fun `reconnecting to connecting on retry`() {
+        stateFlow.value = PlaybackState.Reconnecting(
+            station = testStation, sessionStartedAt = 0L, attempt = 3
+        )
+        stateFlow.value = PlaybackState.Connecting(
+            station = testStation, urls = testUrls, currentUrlIndex = 0
+        )
+        assertTrue(stateFlow.value is PlaybackState.Connecting)
+    }
+
+    @Test
+    fun `reconnecting to idle on user stop`() {
+        stateFlow.value = PlaybackState.Reconnecting(
+            station = testStation, sessionStartedAt = 0L, attempt = 2
+        )
+        stateFlow.value = PlaybackState.Idle
+        assertTrue(stateFlow.value is PlaybackState.Idle)
+    }
+
+    @Test
+    fun `stop from any state returns to idle`() {
+        val states = listOf(
+            PlaybackState.Connecting(station = testStation, urls = testUrls),
+            PlaybackState.Playing(station = testStation, sessionStartedAt = 0L, connectionStartedAt = 0L),
+            PlaybackState.Paused(station = testStation, sessionStartedAt = 0L),
+            PlaybackState.Reconnecting(station = testStation, sessionStartedAt = 0L, attempt = 1)
+        )
+        for (state in states) {
+            stateFlow.value = state
+            stateFlow.value = PlaybackState.Idle
+            assertTrue("Should be Idle after stop from $state", stateFlow.value is PlaybackState.Idle)
+        }
+    }
+}