Basic unit test for Compacting Scanner

db/wal/compacting_scanner.go

@@ -85,7 +85,7 @@ func (c *CompactingScanner) Next() (*Frame, error) {
 		Data:   make([]byte, c.header.PageSize),
 	}
 
-	if _, err := c.readSeeker.Seek(c.frames[c.cIdx].Offset, io.SeekStart); err != nil {
+	if _, err := c.readSeeker.Seek(c.frames[c.cIdx].Offset+WALFrameHeaderSize, io.SeekStart); err != nil {
 		return nil, err
 	}
 	if _, err := io.ReadFull(c.readSeeker, frame.Data); err != nil {

db/wal/compacting_scanner_test.go

@@ -0,0 +1,53 @@
+package wal
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"testing"
+)
+
+func Test_CompactingScanner_Scan(t *testing.T) {
+	b, err := os.ReadFile("testdata/wal-reader/ok/wal")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	s, err := NewCompactingScanner(bytes.NewReader(b))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for i, expF := range []struct {
+		pgno        uint32
+		commit      uint32
+		dataLowIdx  int
+		dataHighIdx int
+	}{
+		{1, 0, 56, 4152},
+		//{2, 2, 4176, 8272}, // This frame is skipped.
+		{2, 2, 8296, 12392},
+	} {
+		f, err := s.Next()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if f.Pgno != expF.pgno {
+			t.Fatalf("expected pgno %d, got %d", expF.pgno, f.Pgno)
+		}
+		if f.Commit != expF.commit {
+			t.Fatalf("expected commit %d, got %d", expF.commit, f.Commit)
+		}
+		if len(f.Data) != 4096 {
+			t.Fatalf("expected data length 4096, got %d", len(f.Data))
+		}
+		if !bytes.Equal(f.Data, b[expF.dataLowIdx:expF.dataHighIdx]) {
+			t.Fatalf("page data mismatch on test %d", i)
+		}
+	}
+
+	_, err = s.Next()
+	if err != io.EOF {
+		t.Fatalf("expected EOF, got %v", err)
+	}
+}