refactor: add cache tests and remove cache merge task (#14)

cache/test.go

@@ -0,0 +1,24 @@
+package cache
+
+import (
+	"github.com/xujiajun/nutsdb"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func newDb(t *testing.T, dir string) *nutsdb.DB {
+	db, err := nutsdb.Open(nutsdb.Options{
+		Dir:                  filepath.Join(os.TempDir(), dir),
+		EntryIdxMode:         nutsdb.HintKeyValAndRAMIdxMode,
+		SegmentSize:          8 * 1024 * 1024,
+		NodeNum:              1,
+		RWMode:               nutsdb.FileIO,
+		SyncEnable:           true,
+		StartFileLoadingMode: nutsdb.MMap,
+	})
+	if err != nil {
+		t.Fatalf("newDb(dir: %v) open error: %v", dir, err)
+	}
+	return db
+}