hi @waxglass2020 

for purchasing, you do record as usual to record all the inventory you will sell and use for testing, its to match between invoice, real stock and bookkeeping.

for the case that you want to record for testing account, i find some relatable article which has same problem like yours, their answer is as below : 

I can help share some information about recording an item that you use internally.

If the items were used personally, then you should not be selling this product to yourself. This item will be considered as an expense and should be non-taxable. However, it would still depend if your state requires you to do so.

In your case, you can do an inventory adjustment to lower the quantity of items taken for personal use. Here's how:

1. Go to the Lists menu and select the Item List.
2. On the Activities tab, click the drop-down arrow and select Adjust Quantity/Value on Hand.
3. Select the Adjustment Account by clicking the drop-down arrow. Please consult your accountant to ensure the account recorded is the right account for your business.
4. Select the item used and record the New Quantity and Qty Difference.
5. Once done, click Save & Close.

full link of the article : 
https://quickbooks.intuit.com/learn-support/en-us/reports-and-accounting/how-do-i-track-damaged-inve...

hope this helps :)