To anyone having issues with the switch from HMAC-SHA1 to HMAC-SHA256 for OAuth 1.0 when using Boomi (Boomi doesn't support 256 for OAuth 1.0). I just got a response from our Boomi account manager:

Our connector team is aware of the issue and is working on a resolution. Customers should not see any issues stemming from NetSuite's deprecation of SHA1 until Aug 16 during Phase 1 of the new NetSuite version release. We hope to have a solution in place for all customers before that date.

Are they aware of the 3 day test window this month? Or have NS postponed it?

I have already asked NetSuite when the Test window is and have also asked Boomi if they'll be able to fix it till then. I wouldn't count on it though.