I work for a gov contractor. "Risk Reduction Tests" are a common thing. What they mean is a test done partway through a program, to validate that the base assumptions for the program are correct and there haven't been any glaring oversights in terms of the feasibility of the project.
Basically, when contractors (Boeing, in this case) win a job from a bid, they don't then just go off for the duration of the contract, and return to the government at the end of the contract and hand over a delivery. There are generally a series of incremental deliverables and tests during the contract to validate that the contractor is actually working on the contract. Risk reduction tests are one of the mid-program deliverables.
Basically, when contractors (Boeing, in this case) win a job from a bid, they don't then just go off for the duration of the contract, and return to the government at the end of the contract and hand over a delivery. There are generally a series of incremental deliverables and tests during the contract to validate that the contractor is actually working on the contract. Risk reduction tests are one of the mid-program deliverables.