cumulativeSum := int64(0)
		for _, p := range oi.partLengths {
			readers = append(readers, NewDummyDataGen(p, cumulativeSum))
			cumulativeSum += p
		}

		refReader := io.LimitReader(ioutilx.NewSkipReader(io.MultiReader(readers...), off), length)
		if ok, msg := cmpReaders(refReader, rec.Body); !ok {
			t.Fatalf("(%s) Object: %s Case %d ByteRange: %s --> data mismatch! (msg: %s)", instanceType, oi.objectName, i+1, byteRange, msg)