Chris DaMour opened SPR-14442 and commented

MockMvcWebConnection calls MockMVC.perform().andReturn().getResponse() but that doesn't work if you are doign async in your controllers, like returning a deferredResult or Single\ etc (probably CompletableFuture as well).

The mockmvc syntax for achieving a result is a bit clunky requiring two calls to perform()..maybe it could be made simpler there

also HtmlUnitRequestBuilder doesn't set async support to true

Affects: 4.3.1

Comment From: spring-projects-issues

Rossen Stoyanchev commented

Indeed the HTML Unit integration for Spring MVC Test doesn't support async requests currently. We'll have to revisit that for 5.0.