feat: add more multi page tests (#28)

pkg/btree/multi.go

@@ -2,6 +2,7 @@ package btree
 
 import (
 	"encoding/binary"
+	"errors"
 	"io"
 )
 
@@ -55,12 +56,20 @@ func (m *LinkedMetaPage) Next() (*LinkedMetaPage, error) {
 }
 
 func (m *LinkedMetaPage) AddNext() (*LinkedMetaPage, error) {
+	// check that the next pointer is zero
+	curr, err := m.Next()
+	if err != nil {
+		return nil, err
+	}
+	if curr != nil {
+		return nil, errors.New("next pointer is not zero")
+	}
 	offset, err := m.rws.Seek(0, io.SeekEnd)
 	if err != nil {
 		return nil, err
 	}
 	next := &LinkedMetaPage{rws: m.rws, offset: uint64(offset)}
-	if err := binary.Write(m.rws, binary.LittleEndian, next.offset); err != nil {
+	if err := next.Reset(); err != nil {
 		return nil, err
 	}
 	// save the next pointer

pkg/btree/multi_test.go

@@ -1,6 +1,9 @@
 package btree
 
-import "testing"
+import (
+	"reflect"
+	"testing"
+)
 
 func TestMultiBPTree(t *testing.T) {
 	t.Run("empty tree", func(t *testing.T) {
@@ -36,4 +39,63 @@ func TestMultiBPTree(t *testing.T) {
 			t.Fatalf("expected length 36, got %d", mp.Length)
 		}
 	})
+
+	t.Run("insert a second page", func(t *testing.T) {
+		b := newSeekableBuffer()
+		tree := NewMultiBPTree(b)
+		if err := tree.Reset(); err != nil {
+			t.Fatal(err)
+		}
+		next1, err := tree.AddNext()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if next1.MemoryPointer().Offset != 36 {
+			t.Fatalf("expected offset 36, got %d", next1)
+		}
+		if next1.MemoryPointer().Length != 36 {
+			t.Fatalf("expected length 36, got %d", next1)
+		}
+		next2, err := next1.AddNext()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if next2.MemoryPointer().Offset != 72 {
+			t.Fatalf("expected offset 72, got %d", next2)
+		}
+		if next2.MemoryPointer().Length != 36 {
+			t.Fatalf("expected length 36, got %d", next2)
+		}
+
+		// check the first page
+		m1, err := tree.Next()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !reflect.DeepEqual(m1.MemoryPointer(), next1.MemoryPointer()) {
+			t.Fatalf("got %v want %v", m1.MemoryPointer(), next1.MemoryPointer())
+		}
+	})
+
+	t.Run("duplicate next pointer", func(t *testing.T) {
+		b := newSeekableBuffer()
+		tree := NewMultiBPTree(b)
+		if err := tree.Reset(); err != nil {
+			t.Fatal(err)
+		}
+		next1, err := tree.AddNext()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if next1.MemoryPointer().Offset != 36 {
+			t.Fatalf("expected offset 36, got %d", next1)
+		}
+		if next1.MemoryPointer().Length != 36 {
+			t.Fatalf("expected length 36, got %d", next1)
+		}
+		_, err = tree.AddNext()
+		if err == nil {
+			t.Fatal("expected error")
+		}
+	})
 }