Absolutely. Its anabolic and androgenic so will have classic effects of raising free/total.testosterone as well as shutting down your hpta. So yes, if you are planning to test your cyp with bloods but add Deca then one could be rising your test but you won't know which. Though to be clear, Deca won't raise your test as high as your Cyp so if you know where you "should be at" from your weekly MG than you could still get an idea, but not perfectly.
Here's how I reference test (for ME):
For example, my current free total test is around 950 on 200mg per week of Cyp. My first bloods were at 443. So, for me, 200mg per week will raise my total test by about 500 points once my blood has stabilized after 6 weeks without a frontload. So if I'm pinning 750 per week it should be around 2000 or above or my gear is underdosed or bunk.
Keep in mind that this conversion rate is not universal and we all will be a little different.
If you find a nice baseline like I did and have another stable reference point than you can definitely make a strong inference about your gear without having it sent to some lab or Jano.