test(page): cover DiskManagerTest, tempFile and PageTest

src/test/kotlin/kestrel/store/page/DiskManagerTest.kt

@@ -0,0 +1,116 @@
+package kestrel.store.page
+
+import java.nio.file.Files
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+class DiskManagerTest {
+    private fun tempFile() = Files.createTempFile("kestrel-disk", ".db").toFile().also { it.deleteOnExit() }
+
+    @Test
+    fun allocatedPagesStartZeroedAndGrowSequentially() {
+        val manager = DiskManager(tempFile())
+        val first = manager.allocatePage()
+        val second = manager.allocatePage()
+        assertEquals(0L, first)
+        assertEquals(1L, second)
+        assertEquals(2L, manager.allocatedPageCount())
+        manager.close()
+    }
+
+    @Test
+    fun writtenPageContentSurvivesReadBack() {
+        val manager = DiskManager(tempFile())
+        val id = manager.allocatePage()
+        val page = Page(id)
+        page.data[0] = 0x42
+        page.data[Page.PAGE_SIZE - 1] = 0x24
+        manager.writePage(page)
+        val reloaded = manager.readPage(id)
+        assertEquals(0x42, reloaded.data[0])
+        assertEquals(0x24, reloaded.data[Page.PAGE_SIZE - 1])
+        manager.close()
+    }
+
+    @Test
+    fun stateSurvivesCloseAndReopen() {
+        val file = tempFile()
+        val manager = DiskManager(file)
+        val id = manager.allocatePage()
+        val page = Page(id)
+        page.data.fill(7)
+        manager.writePage(page)
+        manager.close()
+
+        val reopened = DiskManager(file)
+        assertEquals(1L, reopened.allocatedPageCount())
+        val reloaded = reopened.readPage(id)
+        assertTrue(reloaded.data.all { it == 7.toByte() })
+        reopened.close()
+    }
+
+    @Test
+    fun freedPagesAreRecycledBeforeGrowingTheFile() {
+        val manager = DiskManager(tempFile())
+        val a = manager.allocatePage()
+        val b = manager.allocatePage()
+        manager.freePage(a)
+        val reused = manager.allocatePage()
+        assertEquals(a, reused)
+        assertEquals(2L, manager.allocatedPageCount())
+        val fresh = manager.allocatePage()
+        assertEquals(2L, fresh)
+        assertTrue(b != reused)
+        manager.close()
+    }
+
+    @Test
+    fun freeListSurvivesReopenAndPopsMostRecentlyFreedFirst() {
+        val file = tempFile()
+        val manager = DiskManager(file)
+        val a = manager.allocatePage()
+        val b = manager.allocatePage()
+        manager.freePage(a)
+        manager.freePage(b)
+        manager.close()
+
+        val reopened = DiskManager(file)
+        assertEquals(b, reopened.allocatePage())
+        assertEquals(a, reopened.allocatePage())
+        reopened.close()
+    }
+
+    @Test
+    fun corruptedPageBytesAreDetectedOnRead() {
+        val file = tempFile()
+        val manager = DiskManager(file)
+        val id = manager.allocatePage()
+        val page = Page(id)
+        page.data.fill(9)
+        manager.writePage(page)
+        manager.close()
+
+        // Flip a byte inside the payload region of the physical slot for `id`, after the header slot and checksum.
+        val slotSize = 4 + Page.PAGE_SIZE
+        val offset = (id + 1) * slotSize + 4 + 10
+        val raf = java.io.RandomAccessFile(file, "rw")
+        raf.seek(offset)
+        val original = raf.read()
+        raf.seek(offset)
+        raf.writeByte((original xor 0xFF) and 0xFF)
+        raf.close()
+
+        val reopened = DiskManager(file)
+        assertFailsWith<CorruptPageException> { reopened.readPage(id) }
+        reopened.close()
+    }
+
+    @Test
+    fun readingUnallocatedPageIsRejected() {
+        val manager = DiskManager(tempFile())
+        assertFailsWith<IllegalArgumentException> { manager.readPage(0) }
+        manager.close()
+    }
+}

src/test/kotlin/kestrel/store/page/PageTest.kt

@@ -0,0 +1,29 @@
+package kestrel.store.page
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class PageTest {
+    @Test
+    fun freshPageIsZeroedAndClean() {
+        val page = Page(3)
+        assertEquals(3, page.id)
+        assertEquals(Page.PAGE_SIZE, page.data.size)
+        assertTrue(page.data.all { it == 0.toByte() })
+        assertFalse(page.isDirty)
+        assertEquals(0, page.pinCount)
+    }
+
+    @Test
+    fun resetClearsDataAndDirtyFlagButKeepsId() {
+        val page = Page(1)
+        page.data[0] = 5
+        page.isDirty = true
+        page.reset()
+        assertTrue(page.data.all { it == 0.toByte() })
+        assertFalse(page.isDirty)
+        assertEquals(1, page.id)
+    }
+}