diff --git a/app/src/main/java/com/rosetta/messenger/ui/chats/input/ChatDetailInput.kt b/app/src/main/java/com/rosetta/messenger/ui/chats/input/ChatDetailInput.kt
index d228b0f..819aeb7 100644
--- a/app/src/main/java/com/rosetta/messenger/ui/chats/input/ChatDetailInput.kt
+++ b/app/src/main/java/com/rosetta/messenger/ui/chats/input/ChatDetailInput.kt
@@ -108,7 +108,7 @@ private fun bytesToHexLower(bytes: ByteArray): String {
     return out.toString()
 }
 
-private fun compressVoiceWaves(source: List<Float>, targetLength: Int): List<Float> {
+internal fun compressVoiceWaves(source: List<Float>, targetLength: Int): List<Float> {
     if (targetLength <= 0) return emptyList()
     if (source.isEmpty()) return List(targetLength) { 0f }
     if (source.size == targetLength) return source
@@ -142,7 +142,7 @@ private fun compressVoiceWaves(source: List<Float>, targetLength: Int): List<Flo
     }
 }
 
-private fun formatVoiceRecordTimer(elapsedMs: Long): String {
+internal fun formatVoiceRecordTimer(elapsedMs: Long): String {
     val safeTenths = (elapsedMs.coerceAtLeast(0L) / 100L).toInt()
     val totalSeconds = safeTenths / 10
     val tenths = safeTenths % 10
diff --git a/app/src/test/java/com/rosetta/messenger/ui/chats/input/VoiceRecordHelpersTest.kt b/app/src/test/java/com/rosetta/messenger/ui/chats/input/VoiceRecordHelpersTest.kt
new file mode 100644
index 0000000..74d1f0e
--- /dev/null
+++ b/app/src/test/java/com/rosetta/messenger/ui/chats/input/VoiceRecordHelpersTest.kt
@@ -0,0 +1,65 @@
+package com.rosetta.messenger.ui.chats.input
+
+import org.junit.Assert.*
+import org.junit.Test
+
+class VoiceRecordHelpersTest {
+
+    @Test
+    fun `formatVoiceRecordTimer formats zero`() {
+        assertEquals("0:00,0", formatVoiceRecordTimer(0L))
+    }
+
+    @Test
+    fun `formatVoiceRecordTimer formats 12300ms`() {
+        assertEquals("0:12,3", formatVoiceRecordTimer(12300L))
+    }
+
+    @Test
+    fun `formatVoiceRecordTimer formats 61500ms`() {
+        assertEquals("1:01,5", formatVoiceRecordTimer(61500L))
+    }
+
+    @Test
+    fun `formatVoiceRecordTimer handles negative`() {
+        assertEquals("0:00,0", formatVoiceRecordTimer(-100L))
+    }
+
+    @Test
+    fun `compressVoiceWaves empty source returns zeros`() {
+        val result = compressVoiceWaves(emptyList(), 5)
+        assertEquals(5, result.size)
+        assertTrue(result.all { it == 0f })
+    }
+
+    @Test
+    fun `compressVoiceWaves same size returns same`() {
+        val source = listOf(0.1f, 0.5f, 0.9f)
+        assertEquals(source, compressVoiceWaves(source, 3))
+    }
+
+    @Test
+    fun `compressVoiceWaves downsamples by max`() {
+        val source = listOf(0.1f, 0.8f, 0.3f, 0.9f, 0.2f, 0.7f)
+        val result = compressVoiceWaves(source, 3)
+        assertEquals(3, result.size)
+        assertEquals(0.8f, result[0], 0.01f)
+        assertEquals(0.9f, result[1], 0.01f)
+        assertEquals(0.7f, result[2], 0.01f)
+    }
+
+    @Test
+    fun `compressVoiceWaves target zero returns empty`() {
+        assertEquals(emptyList<Float>(), compressVoiceWaves(listOf(1f), 0))
+    }
+
+    @Test
+    fun `compressVoiceWaves upsamples via interpolation`() {
+        val source = listOf(0.0f, 1.0f)
+        val result = compressVoiceWaves(source, 3)
+        assertEquals(3, result.size)
+        assertEquals(0.0f, result[0], 0.01f)
+        assertEquals(0.5f, result[1], 0.01f)
+        assertEquals(1.0f, result[2], 0.01f)
+    }
+}