The Critical Design Review is the 'point of no return' for a design. Its purpose is to weed out designs that will not meet requirements before they are manufactured at scale.
CDR on Rocket Team
Rocket Team doesn't make products at scale, so CDR has historically been the final design review for Rocket Team. It was typically used to present changes to the design since PDR.
Testing Review (TR) on Rocket Team
In 2016-2017, Rocket Team decided to try a different approach, and used the name 'testing review' to emphasize the focus on testing. The purpose is to validate all the hand-calcs done in PDR empirically. Therefore, every component should be tested by its Testing Review as close to flight conditions as reasonably possible.