@WebFluxTest does not enable auto-configuration for any reactive template engines

[wilkinsona]

Mustache, FreeMarker, and Thymeleaf all support reactive web apps and should be included in @WebFluxTest

[ayudovin]

@wilkinsona, I want to work on it. Please let me know if I can start working on it?

[wilkinsona]

@ayudovin Thanks for asking, @ayudovin. Yes, you can start working on this. A PR would be much appreciated.

[wilkinsona]

Closing in favour of #16170.