diff --git a/backup.go b/backup.go
index 62b7c00..429a0fa 100644
--- a/backup.go
+++ b/backup.go
@@ -129,6 +129,6 @@ func (b *Backup) Remaining() int {
 //
 // https://www.sqlite.org/c3ref/backup_finish.html#sqlite3backuppagecount
 func (b *Backup) PageCount() int {
-	r := b.c.call(b.c.api.backupFinish, uint64(b.handle))
+	r := b.c.call(b.c.api.backupPageCount, uint64(b.handle))
 	return int(r[0])
 }
diff --git a/sqlite3vfs/reader_test.go b/sqlite3vfs/reader_test.go
index 786e71d..192d6aa 100644
--- a/sqlite3vfs/reader_test.go
+++ b/sqlite3vfs/reader_test.go
@@ -4,7 +4,14 @@ import (
 	"database/sql"
 	"fmt"
 	"log"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
 
+	_ "embed"
+
+	"github.com/ncruces/go-sqlite3"
 	_ "github.com/ncruces/go-sqlite3/driver"
 	_ "github.com/ncruces/go-sqlite3/embed"
 	"github.com/ncruces/go-sqlite3/sqlite3vfs"
@@ -58,3 +65,85 @@ func ExampleReaderVFS() {
 	// 2012.03: 18477 million Dollars
 	// 2012.06: 18270 million Dollars
 }
+
+//go:embed testdata/test.db
+var testDB string
+
+func TestReaderVFS_Open(t *testing.T) {
+	sqlite3vfs.Register("reader", sqlite3vfs.ReaderVFS{
+		"test.db": sqlite3vfs.NewSizeReaderAt(strings.NewReader(testDB)),
+	})
+
+	_, err := sqlite3.Open("file:demo.db?vfs=reader&mode=ro")
+	if err == nil {
+		t.Error("want error")
+	}
+
+	db, err := sqlite3.Open("file:test.db?vfs=reader&mode=ro")
+	if err != nil {
+		t.Error(err)
+	}
+	defer db.Close()
+
+	stmt, _, err := db.Prepare(`SELECT id, name FROM users`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer stmt.Close()
+
+	row := 0
+	ids := []int{0, 1, 2}
+	names := []string{"go", "zig", "whatever"}
+	for ; stmt.Step(); row++ {
+		id := stmt.ColumnInt(0)
+		name := stmt.ColumnText(1)
+
+		if id != ids[row] {
+			t.Errorf("got %d, want %d", id, ids[row])
+		}
+		if name != names[row] {
+			t.Errorf("got %q, want %q", name, names[row])
+		}
+	}
+	if row != 3 {
+		t.Errorf("got %d, want %d", row, len(ids))
+	}
+
+	if err := stmt.Err(); err != nil {
+		t.Fatal(err)
+	}
+
+	err = stmt.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = db.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestNewSizeReaderAt(t *testing.T) {
+	n, err := sqlite3vfs.NewSizeReaderAt(strings.NewReader("abc")).Size()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 3 {
+		t.Errorf("got %d", n)
+	}
+
+	f, err := os.Create(filepath.Join(t.TempDir(), "abc.txt"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	n, err = sqlite3vfs.NewSizeReaderAt(f).Size()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 0 {
+		t.Errorf("got %d", n)
+	}
+}
diff --git a/sqlite3vfs/testdata/test.db b/sqlite3vfs/testdata/test.db
new file mode 100644
index 0000000..48ea4e7
Binary files /dev/null and b/sqlite3vfs/testdata/test.db differ
diff --git a/sqlite3vfs/vfs_test.go b/sqlite3vfs/vfs_test.go
index d794451..56dc105 100644
--- a/sqlite3vfs/vfs_test.go
+++ b/sqlite3vfs/vfs_test.go
@@ -198,6 +198,15 @@ func Test_vfsAccess(t *testing.T) {
 		t.Error("can't access directory")
 	}
 
+	util.WriteString(mod, 8, file)
+	rc = vfsAccess(ctx, mod, 0, 8, ACCESS_READ, 4)
+	if rc != _OK {
+		t.Fatal("returned", rc)
+	}
+	if got := util.ReadUint32(mod, 4); got != 1 {
+		t.Error("can't access file")
+	}
+
 	util.WriteString(mod, 8, file)
 	rc = vfsAccess(ctx, mod, 0, 8, ACCESS_READWRITE, 4)
 	if rc != _OK {
diff --git a/tests/backup_test.go b/tests/backup_test.go
index cc3fbec..1d3d0a8 100644
--- a/tests/backup_test.go
+++ b/tests/backup_test.go
@@ -124,4 +124,46 @@ func TestBackup(t *testing.T) {
 			t.Fatal(err)
 		}
 	}()
+
+	func() { // Incremental.
+		db, err := sqlite3.Open(backupName)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer db.Close()
+
+		b, err := db.BackupInit("main", ":memory:")
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer b.Close()
+
+		done, err := b.Step(1)
+		if done {
+			t.Error("want false")
+		}
+		if err != nil {
+			t.Error(err)
+		}
+
+		n := b.Remaining()
+		if n != 1 {
+			t.Errorf("got %d", n)
+		}
+
+		n = b.PageCount()
+		if n != 2 {
+			t.Errorf("got %d", n)
+		}
+
+		err = b.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		err = db.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+	}()
 }
diff --git a/tests/driver_test.go b/tests/driver_test.go
index 732dc17..94a5c97 100644
--- a/tests/driver_test.go
+++ b/tests/driver_test.go
@@ -27,18 +27,32 @@ func TestDriver(t *testing.T) {
 	}
 	defer conn.Close()
 
-	_, err = conn.ExecContext(ctx,
+	res, err := conn.ExecContext(ctx,
 		`CREATE TABLE IF NOT EXISTS users (id INT, name VARCHAR(10))`)
 	if err != nil {
 		t.Fatal(err)
 	}
+	changes, err := res.RowsAffected()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if changes != 0 {
+		t.Errorf("got %d want 0", changes)
+	}
+	id, err := res.LastInsertId()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if id != 0 {
+		t.Errorf("got %d want 0", changes)
+	}
 
-	res, err := conn.ExecContext(ctx,
+	res, err = conn.ExecContext(ctx,
 		`INSERT INTO users (id, name) VALUES (0, 'go'), (1, 'zig'), (2, 'whatever')`)
 	if err != nil {
 		t.Fatal(err)
 	}
-	changes, err := res.RowsAffected()
+	changes, err = res.RowsAffected()
 	if err != nil {
 		t.Fatal(err)
 	}