If you have not been asked to complete a duct test by your local Building Inspector, it is just a matter of time before you are surprised by this code requirement. Despite some push-back from city and town Inspectors, all of MA (and the country per Residential Code) is required to test new or altered duct systems - with varying enforcement, and held to various degrees of leakage rates. This has been in place since the 2009 International Energy Conservation Code (IECC) back in 2010. It pays to know which towns you are working in, and their permit structure, to avoid losing what could amount to be a significant part of your profit on these jobs.
If you are working in most of the cities and towns across the state, you are able to complete your own "Total Leakage Duct Test". If a building permit was pulled as part of an addition or new construction building, third-party testing by a RESNET Certified HERS Rater will be required. This means that even if you went and got your certification, you could not test your own for these jobs anyhow. Don't worry though, a HERS Rater is needed to rate the home or addition, and their testing is not exclusive to your duct system. This means a rating is needed when a Building Permit is pulled, a change to a structural wall. In other words, as long as the testing does not fail due to your duct system, the general contractor will be paying for this rating.
Anyhow, take a look at the attached document I created, I think it will help those that are just becoming involved with Duct Testing.
2021 International Energy Conservation Code
R403.3.6 Duct Leakage