test(heap): cover HeapPageTest and freshPage

src/test/kotlin/kestrel/store/heap/HeapPageTest.kt

@@ -0,0 +1,139 @@
+package kestrel.store.heap
+
+import kestrel.store.page.Page
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+class HeapPageTest {
+    private fun freshPage(): Page = Page(0).also { HeapPage.init(it) }
+
+    @Test
+    fun freshPageHasNoSlotsAndFullFreeSpace() {
+        val page = freshPage()
+        assertEquals(0, HeapPage.slotCount(page))
+        assertEquals(HeapPage.NO_PAGE, HeapPage.nextPageId(page))
+        assertTrue(HeapPage.freeBytes(page) > HeapPage.MAX_RECORD_SIZE)
+    }
+
+    @Test
+    fun insertAndGetRoundTrips() {
+        val page = freshPage()
+        val slot = HeapPage.insert(page, "hello".toByteArray())
+        assertEquals(0, slot)
+        assertEquals("hello", String(HeapPage.get(page, slot!!)))
+    }
+
+    @Test
+    fun multipleSlotsPreserveIndependentContent() {
+        val page = freshPage()
+        val a = HeapPage.insert(page, "alpha".toByteArray())!!
+        val b = HeapPage.insert(page, "beta".toByteArray())!!
+        val c = HeapPage.insert(page, "gamma".toByteArray())!!
+        assertEquals("alpha", String(HeapPage.get(page, a)))
+        assertEquals("beta", String(HeapPage.get(page, b)))
+        assertEquals("gamma", String(HeapPage.get(page, c)))
+    }
+
+    @Test
+    fun freeBytesShrinksAsRecordsAreInserted() {
+        val page = freshPage()
+        val before = HeapPage.freeBytes(page)
+        HeapPage.insert(page, ByteArray(100))
+        val after = HeapPage.freeBytes(page)
+        assertEquals(100 + 4, before - after)
+    }
+
+    @Test
+    fun insertReturnsNullWhenPageIsFull() {
+        val page = freshPage()
+        var last: Int? = 0
+        while (last != null) {
+            last = HeapPage.insert(page, ByteArray(200))
+        }
+        assertNull(HeapPage.insert(page, ByteArray(200)))
+    }
+
+    @Test
+    fun deleteTombstonesSlotAndGetThrows() {
+        val page = freshPage()
+        val slot = HeapPage.insert(page, "doomed".toByteArray())!!
+        HeapPage.delete(page, slot)
+        assertTrue(HeapPage.isDeleted(page, slot))
+        assertFailsWith<HeapPageException> { HeapPage.get(page, slot) }
+    }
+
+    @Test
+    fun deletingAlreadyDeletedSlotFails() {
+        val page = freshPage()
+        val slot = HeapPage.insert(page, "x".toByteArray())!!
+        HeapPage.delete(page, slot)
+        assertFailsWith<HeapPageException> { HeapPage.delete(page, slot) }
+    }
+
+    @Test
+    fun compactReclaimsSpaceFromDeletedSlots() {
+        val page = freshPage()
+        val slots = ArrayList<Int>()
+        while (true) {
+            val slot = HeapPage.insert(page, ByteArray(250)) ?: break
+            slots.add(slot)
+        }
+        for (slot in slots.take(slots.size / 2)) HeapPage.delete(page, slot)
+        // Freed space is fragmented (tombstoned), not contiguous, until compact runs from within insert.
+        assertTrue(HeapPage.insert(page, ByteArray(250)) != null)
+    }
+
+    @Test
+    fun compactPreservesLiveSlotIdsAndContent() {
+        val page = freshPage()
+        val a = HeapPage.insert(page, "keep-a".toByteArray())!!
+        val b = HeapPage.insert(page, "gone".toByteArray())!!
+        val c = HeapPage.insert(page, "keep-c".toByteArray())!!
+        HeapPage.delete(page, b)
+        HeapPage.compact(page)
+        assertEquals("keep-a", String(HeapPage.get(page, a)))
+        assertEquals("keep-c", String(HeapPage.get(page, c)))
+        assertTrue(HeapPage.isDeleted(page, b))
+    }
+
+    @Test
+    fun overwriteInPlaceShrinksLength() {
+        val page = freshPage()
+        val slot = HeapPage.insert(page, "original-value".toByteArray())!!
+        HeapPage.overwrite(page, slot, "short".toByteArray())
+        assertEquals("short", String(HeapPage.get(page, slot)))
+        assertEquals(5, HeapPage.lengthOf(page, slot))
+    }
+
+    @Test
+    fun overwriteGrowingBeyondCapacityFails() {
+        val page = freshPage()
+        val slot = HeapPage.insert(page, "short".toByteArray())!!
+        assertFailsWith<IllegalArgumentException> { HeapPage.overwrite(page, slot, "much-longer-value".toByteArray()) }
+    }
+
+    @Test
+    fun accessingOutOfRangeSlotFails() {
+        val page = freshPage()
+        assertFailsWith<HeapPageException> { HeapPage.get(page, 0) }
+        assertFailsWith<HeapPageException> { HeapPage.get(page, -1) }
+    }
+
+    @Test
+    fun insertRejectsRecordLargerThanPage() {
+        val page = freshPage()
+        assertFailsWith<IllegalArgumentException> { HeapPage.insert(page, ByteArray(HeapPage.MAX_RECORD_SIZE + 1)) }
+    }
+
+    @Test
+    fun setNextPageIdRoundTripsAndMarksPageDirty() {
+        val page = freshPage()
+        page.isDirty = false
+        HeapPage.setNextPageId(page, 42L)
+        assertEquals(42L, HeapPage.nextPageId(page))
+        assertTrue(page.isDirty)
+    }
+}