diff --git a/src/test/kotlin/kestrel/store/wal/WriteAheadLogTest.kt b/src/test/kotlin/kestrel/store/wal/WriteAheadLogTest.kt
new file mode 100644
index 0000000..4efb686
--- /dev/null
+++ b/src/test/kotlin/kestrel/store/wal/WriteAheadLogTest.kt
@@ -0,0 +1,128 @@
+package kestrel.store.wal
+
+import java.io.File
+import java.io.RandomAccessFile
+import java.nio.file.Files
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+class WriteAheadLogTest {
+    private fun tempFile(): File = Files.createTempFile("kestrel-wal", ".log").toFile().also { it.deleteOnExit() }
+
+    @Test
+    fun beginAssignsIncreasingTransactionIds() {
+        val wal = WriteAheadLog(tempFile())
+        val a = wal.beginTransaction()
+        val b = wal.beginTransaction()
+        assertTrue(b > a)
+        wal.close()
+    }
+
+    @Test
+    fun logUpdateChainsPrevLsnToTheTransactionsPriorRecord() {
+        val wal = WriteAheadLog(tempFile())
+        val txn = wal.beginTransaction()
+        val beginLsn = wal.lastLsnOf(txn)
+        val firstUpdateLsn = wal.logUpdate(txn, 0L, ByteArray(1), ByteArray(1))
+        val secondUpdateLsn = wal.logUpdate(txn, 0L, ByteArray(1), ByteArray(1))
+
+        val firstRecord = wal.readAt(firstUpdateLsn) as LogRecord.Update
+        val secondRecord = wal.readAt(secondUpdateLsn) as LogRecord.Update
+        assertEquals(beginLsn, firstRecord.prevLsn)
+        assertEquals(firstUpdateLsn, secondRecord.prevLsn)
+        wal.close()
+    }
+
+    @Test
+    fun commitClearsActiveTrackingForTheTransaction() {
+        val wal = WriteAheadLog(tempFile())
+        val txn = wal.beginTransaction()
+        wal.commit(txn)
+        assertEquals(WriteAheadLog.NO_LSN, wal.lastLsnOf(txn))
+        wal.close()
+    }
+
+    @Test
+    fun loggingUpdateForUnknownTransactionFails() {
+        val wal = WriteAheadLog(tempFile())
+        assertFailsWith<WalException> { wal.logUpdate(999L, 0L, ByteArray(1), ByteArray(1)) }
+        wal.close()
+    }
+
+    @Test
+    fun checkpointRejectsActiveTransactions() {
+        val wal = WriteAheadLog(tempFile())
+        wal.beginTransaction()
+        assertFailsWith<IllegalStateException> { wal.checkpoint() }
+        wal.close()
+    }
+
+    @Test
+    fun checkpointIsRecordedAsLastCheckpointLsn() {
+        val wal = WriteAheadLog(tempFile())
+        val txn = wal.beginTransaction()
+        wal.commit(txn)
+        val checkpointLsn = wal.checkpoint()
+        assertEquals(checkpointLsn, wal.lastCheckpointLsn)
+        wal.close()
+    }
+
+    @Test
+    fun readFromReturnsRecordsInLogOrder() {
+        val wal = WriteAheadLog(tempFile())
+        val txn = wal.beginTransaction()
+        wal.logUpdate(txn, 1L, ByteArray(1), ByteArray(1))
+        wal.commit(txn)
+        val records = wal.readFrom(0L).map { it.second }
+        assertTrue(records[0] is LogRecord.Begin)
+        assertTrue(records[1] is LogRecord.Update)
+        assertTrue(records[2] is LogRecord.Commit)
+        wal.close()
+    }
+
+    @Test
+    fun reopeningResumesTransactionIdsPastThoseAlreadyLogged() {
+        val file = tempFile()
+        val first = WriteAheadLog(file)
+        val txn = first.beginTransaction()
+        first.commit(txn)
+        first.close()
+
+        val reopened = WriteAheadLog(file)
+        val nextTxn = reopened.beginTransaction()
+        assertTrue(nextTxn > txn)
+        reopened.close()
+    }
+
+    @Test
+    fun reopeningRecoversLastCheckpointLsn() {
+        val file = tempFile()
+        val first = WriteAheadLog(file)
+        val txn = first.beginTransaction()
+        first.commit(txn)
+        val checkpointLsn = first.checkpoint()
+        first.close()
+
+        val reopened = WriteAheadLog(file)
+        assertEquals(checkpointLsn, reopened.lastCheckpointLsn)
+        reopened.close()
+    }
+
+    @Test
+    fun corruptedFrameFailsChecksumValidation() {
+        val file = tempFile()
+        val wal = WriteAheadLog(file)
+        val txn = wal.beginTransaction()
+        wal.commit(txn)
+        wal.close()
+
+        RandomAccessFile(file, "rw").use { raf ->
+            raf.seek(10)
+            raf.write(0xFF)
+        }
+
+        assertFailsWith<WalCorruptionException> { WriteAheadLog(file) }
+    }
+}