Hi Billy, great question. I do cover testing Reactor (WebFlux) based Spring Boot applications using
JUnit 5, and I discuss some of the concerns (gotchas?) of unit testing reactive streams capabilities vis-a-vis "standard Java" functionality. I guess that counts as new tactics (to some extent), but certainly not a new testing strategy; testing strategy as a whole doesn't change whether the app blocks or doesn't, IMO.
I focused on Boot, various Spring team-supported components, and a very few community/external options, so I didn't directly address Ratpack. Many of the concepts in the reactive chapters of course have applicability, but some mental mapping would of course be required.
Hope this helps,
Mark