Add edge-case + stress test battery (14 tests)

Empty files, 20MB large file (byte-intact round-trip), 8-level deep nesting,
unicode folder names, 200-char filenames, no-extension files, idempotency/loop
guard (repeated syncs upload nothing), bulk update/delete/download (10 each),
KEEP_BOTH conflict, min-size + include-extension filters, whole-folder wipe.
All green on a Galaxy S23 against live Nextcloud.

app/src/androidTest/kotlin/com/syncflow/FullSyncEngineTest.kt

@@ -73,8 +73,10 @@ class FullSyncEngineTest {
         conflict: ConflictStrategy = ConflictStrategy.KEEP_NEWEST,
         recursive: Boolean = true,
         excludeExtensions: String = "",
+        includeExtensions: String = "",
         excludePatterns: String = "",
         skipHidden: Boolean = false,
+        minKb: Long = 0L,
         maxKb: Long = 0L,
     ): Triple<SyncPair, File, String> {
         val local = File(ctx.cacheDir, "synctest_${name}_${System.currentTimeMillis()}").apply { mkdirs() }
@@ -86,8 +88,8 @@ class FullSyncEngineTest {
             syncDirection = dir, conflictStrategy = conflict, deleteBehavior = delete, recursive = recursive,
             scheduleType = ScheduleType.MANUAL, scheduleIntervalMinutes = 30, scheduleDailyTime = null, scheduleWeekdays = 0,
             wifiOnly = false, wifiSsid = "", chargingOnly = false, minBatteryPct = 0,
-            excludePatterns = excludePatterns, includeExtensions = "", excludeExtensions = excludeExtensions,
+            excludePatterns = excludePatterns, includeExtensions = includeExtensions, excludeExtensions = excludeExtensions,
-            skipHiddenFiles = skipHidden, minFileSizeKb = 0, maxFileSizeKb = maxKb,
+            skipHiddenFiles = skipHidden, minFileSizeKb = minKb, maxFileSizeKb = maxKb,
             notifyOnComplete = false, notifyOnError = false,
             isEnabled = true, lastSyncAt = null, lastSyncResult = SyncStatus.IDLE, pendingConflicts = 0,
         ))
@@ -277,4 +279,145 @@ class FullSyncEngineTest {
         write(local, "big.txt", payload); sync(pair)
         assertEquals(payload, remoteText("$remote/big.txt"))
     }
+
+    // ══ EDGE CASES & STRESS ═══════════════════════════════════════════════════
+
+    private fun writeBytes(dir: File, rel: String, bytes: ByteArray) =
+        File(dir, rel).apply { parentFile?.mkdirs() }.writeBytes(bytes)
+
+    // 15. Empty (0-byte) file uploads correctly
+    @Test fun emptyFile_uploads() = runBlocking {
+        val (pair, local, remote) = newPair("empty", SyncDirection.UPLOAD_ONLY, DeleteBehavior.KEEP)
+        write(local, "zero.txt", "")
+        val r = sync(pair)
+        assertEquals(0, r.failedFiles); assertEquals(1, r.uploaded)
+        assertEquals(0L, provider.listFiles(remote).getOrThrow().first { it.name == "zero.txt" }.sizeBytes)
+    }
+
+    // 16. Large file (20 MB) uploads + downloads byte-intact (OOM / streaming guard)
+    @Test fun largeFile_intactRoundTrip() = runBlocking {
+        val (pair, local, remote) = newPair("large", SyncDirection.UPLOAD_ONLY, DeleteBehavior.KEEP)
+        val size = 20 * 1024 * 1024
+        val bytes = ByteArray(size).also { java.util.Random(42).nextBytes(it) }
+        writeBytes(local, "big.bin", bytes)
+        val r = sync(pair)
+        assertEquals(0, r.failedFiles); assertEquals(1, r.uploaded)
+        assertEquals(size.toLong(), provider.listFiles(remote).getOrThrow().first { it.name == "big.bin" }.sizeBytes)
+        val out = ByteArrayOutputStream(size); provider.downloadFile("$remote/big.bin", out).getOrThrow()
+        val dl = out.toByteArray()
+        assertEquals(size, dl.size)
+        assertArrayEquals(bytes.copyOfRange(0, 4096), dl.copyOfRange(0, 4096))
+        assertArrayEquals(bytes.copyOfRange(size - 4096, size), dl.copyOfRange(size - 4096, size))
+    }
+
+    // 17. Deeply nested path (8 levels) is created + uploaded
+    @Test fun deepNesting_uploads() = runBlocking {
+        val (pair, local, remote) = newPair("deep", SyncDirection.UPLOAD_ONLY, recursive = true)
+        write(local, "a/b/c/d/e/f/g/deep.txt", "deep")
+        assertEquals(0, sync(pair).failedFiles)
+        assertTrue("deep.txt" in remoteNames("$remote/a/b/c/d/e/f/g"))
+    }
+
+    // 18. Unicode FOLDER names (not just files) are created + encoded
+    @Test fun unicodeFolderNames_upload() = runBlocking {
+        val (pair, local, remote) = newPair("ufolder", SyncDirection.UPLOAD_ONLY, recursive = true)
+        write(local, "Фото/café/x.txt", "u")
+        assertEquals(0, sync(pair).failedFiles)
+        assertTrue("x.txt" in remoteNames("$remote/Фото/café"))
+    }
+
+    // 19. Very long filename (200 chars)
+    @Test fun veryLongFilename_uploads() = runBlocking {
+        val (pair, local, remote) = newPair("longname", SyncDirection.UPLOAD_ONLY, DeleteBehavior.KEEP)
+        val name = "L".repeat(200) + ".txt"
+        write(local, name, "x")
+        assertEquals(0, sync(pair).failedFiles)
+        assertTrue(name in remoteNames(remote))
+    }
+
+    // 20. File with no extension
+    @Test fun noExtensionFile_uploads() = runBlocking {
+        val (pair, local, remote) = newPair("noext", SyncDirection.UPLOAD_ONLY, DeleteBehavior.KEEP)
+        write(local, "README", "x")
+        assertEquals(1, sync(pair).uploaded)
+        assertTrue("README" in remoteNames(remote))
+    }
+
+    // 21. Idempotency / loop guard — repeated syncs do NOT re-upload anything
+    @Test fun idempotent_repeatedSyncsNoPhantomUploads() = runBlocking {
+        val (pair, local, remote) = newPair("idem", SyncDirection.UPLOAD_ONLY, DeleteBehavior.KEEP)
+        repeat(10) { i -> write(local, "x_$i.txt", "v$i") }
+        assertEquals(10, sync(pair).uploaded)
+        repeat(4) {
+            val r = sync(pair)
+            assertEquals("sync must be idempotent (no re-upload loop)", 0, r.uploaded)
+            assertEquals(0, r.deleted); assertEquals(0, r.failedFiles)
+        }
+    }
+
+    // 22. Bulk update — modifying many files re-uploads exactly those
+    @Test fun bulkUpdate_reuploadsChanged() = runBlocking {
+        val (pair, local, remote) = newPair("bulkupd", SyncDirection.UPLOAD_ONLY, DeleteBehavior.KEEP)
+        repeat(10) { i -> write(local, "u_$i.txt", "v1") }; sync(pair)
+        Thread.sleep(1100)
+        repeat(10) { i -> write(local, "u_$i.txt", "v2-updated-content") }
+        assertEquals(10, sync(pair).uploaded)
+        assertEquals("v2-updated-content", remoteText("$remote/u_0.txt"))
+    }
+
+    // 23. Bulk delete (MIRROR two-way) propagates all deletions
+    @Test fun mirror_bulkDeletePropagates() = runBlocking {
+        val (pair, local, remote) = newPair("bulkdel", SyncDirection.TWO_WAY, DeleteBehavior.MIRROR)
+        repeat(10) { i -> write(local, "d_$i.txt", "x") }; sync(pair)
+        repeat(10) { i -> File(local, "d_$i.txt").delete() }
+        assertEquals(10, sync(pair).deleted)
+        assertEquals(0, remoteNames(remote).count { it.startsWith("d_") })
+    }
+
+    // 24. Bulk download (download-only) pulls all remote files
+    @Test fun downloadOnly_bulkPull() = runBlocking {
+        val (pair, local, remote) = newPair("bulkdl", SyncDirection.DOWNLOAD_ONLY)
+        repeat(10) { i -> putRemote(remote, "r_$i.txt", "cloud$i") }
+        assertEquals(10, sync(pair).downloaded)
+        assertEquals(10, local.listFiles()!!.count { it.name.startsWith("r_") })
+    }
+
+    // 25. KEEP_BOTH conflict strategy records a conflict (no silent clobber)
+    @Test fun twoWay_keepBoth_recordsConflict() = runBlocking {
+        val (pair, local, remote) = newPair("keepboth", SyncDirection.TWO_WAY, conflict = ConflictStrategy.KEEP_BOTH)
+        write(local, "c.txt", "base"); sync(pair); sync(pair) // baseline + reconcile
+        Thread.sleep(1100)
+        write(local, "c.txt", "LOCAL"); putRemote(remote, "c.txt", "REMOTE")
+        assertEquals(1, sync(pair).conflicts)
+        assertEquals("LOCAL", File(local, "c.txt").readText())
+        assertEquals("REMOTE", remoteText("$remote/c.txt"))
+    }
+
+    // 26. Min-size filter skips tiny files
+    @Test fun filters_minSizeSkipsTiny() = runBlocking {
+        val (pair, local, remote) = newPair("minsize", SyncDirection.UPLOAD_ONLY, minKb = 1)
+        write(local, "tiny.txt", "x")                       // < 1 KB
+        write(local, "big.txt", "A".repeat(2048))           // ~2 KB
+        sync(pair)
+        val n = remoteNames(remote)
+        assertFalse("tiny.txt" in n); assertTrue("big.txt" in n)
+    }
+
+    // 27. Include-extension filter uploads only matching files
+    @Test fun filters_includeExtensionOnly() = runBlocking {
+        val (pair, local, remote) = newPair("incl", SyncDirection.UPLOAD_ONLY, includeExtensions = "jpg")
+        write(local, "keep.jpg", "x"); write(local, "skip.txt", "y")
+        sync(pair)
+        val n = remoteNames(remote)
+        assertTrue("keep.jpg" in n); assertFalse("skip.txt" in n)
+    }
+
+    // 28. Whole-folder wipe locally (MIRROR) removes all remote copies
+    @Test fun mirror_emptyLocalWipesRemote() = runBlocking {
+        val (pair, local, remote) = newPair("wipe", SyncDirection.TWO_WAY, DeleteBehavior.MIRROR)
+        repeat(5) { i -> write(local, "w_$i.txt", "x") }; sync(pair)
+        local.listFiles()!!.forEach { it.delete() }
+        assertEquals(5, sync(pair).deleted)
+        assertEquals(0, remoteNames(remote).count { it.startsWith("w_") })
+    }
 }