test(wal): cover LogRecordCodecTest and beginRoundTrips

src/test/kotlin/kestrel/store/wal/LogRecordCodecTest.kt

@@ -0,0 +1,75 @@
+package kestrel.store.wal
+
+import kotlin.test.Test
+import kotlin.test.assertContentEquals
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+class LogRecordCodecTest {
+    @Test
+    fun beginRoundTrips() {
+        val decoded = LogRecordCodec.decode(LogRecordCodec.encode(LogRecord.Begin(7L)))
+        assertTrue(decoded is LogRecord.Begin)
+        assertEquals(7L, decoded.txnId)
+    }
+
+    @Test
+    fun commitRoundTrips() {
+        val decoded = LogRecordCodec.decode(LogRecordCodec.encode(LogRecord.Commit(9L)))
+        assertTrue(decoded is LogRecord.Commit)
+        assertEquals(9L, decoded.txnId)
+    }
+
+    @Test
+    fun abortRoundTrips() {
+        val decoded = LogRecordCodec.decode(LogRecordCodec.encode(LogRecord.Abort(3L)))
+        assertTrue(decoded is LogRecord.Abort)
+        assertEquals(3L, decoded.txnId)
+    }
+
+    @Test
+    fun updateRoundTripsPageImagesAndChainPointer() {
+        val before = ByteArray(4096) { 1 }
+        val after = ByteArray(4096) { 2 }
+        val original = LogRecord.Update(txnId = 5L, prevLsn = 128L, pageId = 42L, before = before, after = after)
+        val decoded = LogRecordCodec.decode(LogRecordCodec.encode(original))
+        assertTrue(decoded is LogRecord.Update)
+        assertEquals(5L, decoded.txnId)
+        assertEquals(128L, decoded.prevLsn)
+        assertEquals(42L, decoded.pageId)
+        assertContentEquals(before, decoded.before)
+        assertContentEquals(after, decoded.after)
+    }
+
+    @Test
+    fun compensationUpdateRoundTripsUndoImageAndSkipPointer() {
+        val undoImage = ByteArray(4096) { 3 }
+        val original = LogRecord.CompensationUpdate(
+            txnId = 11L,
+            prevLsn = 256L,
+            pageId = 17L,
+            undoImage = undoImage,
+            undoNextLsn = 64L
+        )
+        val decoded = LogRecordCodec.decode(LogRecordCodec.encode(original))
+        assertTrue(decoded is LogRecord.CompensationUpdate)
+        assertEquals(11L, decoded.txnId)
+        assertEquals(256L, decoded.prevLsn)
+        assertEquals(17L, decoded.pageId)
+        assertContentEquals(undoImage, decoded.undoImage)
+        assertEquals(64L, decoded.undoNextLsn)
+    }
+
+    @Test
+    fun checkpointRoundTripsActiveTxnList() {
+        val decoded = LogRecordCodec.decode(LogRecordCodec.encode(LogRecord.Checkpoint(listOf(1L, 2L, 3L))))
+        assertTrue(decoded is LogRecord.Checkpoint)
+        assertEquals(listOf(1L, 2L, 3L), decoded.activeTxnIds)
+    }
+
+    @Test
+    fun decodingUnknownTypeTagFails() {
+        assertFailsWith<WalCorruptionException> { LogRecordCodec.decode(byteArrayOf(99)) }
+    }
+}