test: cover MIME type normalization for MediaStore

Verify video/x-m4v maps to video/mp4 (the failing case), normalization
is case-insensitive, and supported image/video/audio types pass through
unchanged. Required making normalizeMimeTypeForMediaStore internal.

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/actions/MediaSaverToDisk.kt

@@ -274,7 +274,7 @@ object MediaSaverToDisk {
     // Android's MediaStore only accepts a fixed allow-list of MIME types.
     // MimeTypeMap returns variants like video/x-m4v that MediaProvider rejects,
     // so map them to the closest supported equivalent.
-    private fun normalizeMimeTypeForMediaStore(mimeType: String): String =
+    internal fun normalizeMimeTypeForMediaStore(mimeType: String): String =
         when (mimeType.lowercase()) {
             "video/x-m4v" -> "video/mp4"
             else -> mimeType

amethyst/src/test/java/com/vitorpamplona/amethyst/ui/actions/MediaSaverToDiskTest.kt

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.ui.actions
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class MediaSaverToDiskTest {
+    @Test
+    fun normalizesVideoXM4vToVideoMp4() {
+        assertEquals("video/mp4", MediaSaverToDisk.normalizeMimeTypeForMediaStore("video/x-m4v"))
+    }
+
+    @Test
+    fun normalizationIsCaseInsensitive() {
+        assertEquals("video/mp4", MediaSaverToDisk.normalizeMimeTypeForMediaStore("Video/X-M4V"))
+    }
+
+    @Test
+    fun passesThroughSupportedVideoTypes() {
+        assertEquals("video/mp4", MediaSaverToDisk.normalizeMimeTypeForMediaStore("video/mp4"))
+        assertEquals("video/webm", MediaSaverToDisk.normalizeMimeTypeForMediaStore("video/webm"))
+        assertEquals("video/quicktime", MediaSaverToDisk.normalizeMimeTypeForMediaStore("video/quicktime"))
+    }
+
+    @Test
+    fun passesThroughImageAndAudioTypes() {
+        assertEquals("image/jpeg", MediaSaverToDisk.normalizeMimeTypeForMediaStore("image/jpeg"))
+        assertEquals("image/png", MediaSaverToDisk.normalizeMimeTypeForMediaStore("image/png"))
+        assertEquals("audio/mpeg", MediaSaverToDisk.normalizeMimeTypeForMediaStore("audio/mpeg"))
+    }
+}