Add support for asyncDispatch to MockMvc Kotlin DSL

Closes gh-23758

spring-test/src/main/kotlin/org/springframework/test/web/servlet/MockHttpServletRequestDsl.kt

@@ -204,6 +204,6 @@ open class MockHttpServletRequestDsl(private val builder: MockHttpServletRequest
 		flashAttrs?.also { builder.flashAttrs(flashAttrs!!) }
 		session?.also { builder.session(session!!) }
 		principal?.also { builder.principal(principal!!) }
-		return ResultActionsDsl(mockMvc.perform(builder))
+		return ResultActionsDsl(mockMvc.perform(builder), mockMvc)
 	}
 }

spring-test/src/main/kotlin/org/springframework/test/web/servlet/ResultActionsDsl.kt

 package org.springframework.test.web.servlet
 
+import org.springframework.test.web.servlet.request.MockMvcRequestBuilders
+
 /**
  * Provide a [ResultActions] Kotlin DSL in order to be able to write idiomatic Kotlin code.
  *
  * @author Sebastien Deleuze
  * @since 5.2
  */
-class ResultActionsDsl(private val actions: ResultActions) {
+class ResultActionsDsl(private val actions: ResultActions, private val mockMvc: MockMvc) {
 
 	/**
 	 * Provide access to [MockMvcResultMatchersDsl] Kotlin DSL.
@@ -26,6 +28,19 @@ class ResultActionsDsl(private val actions: ResultActions) {
 		return this
 	}
 
+	/**
+	 * Enable asynchronous dispatching.
+	 * @see MockMvcRequestBuilders.asyncDispatch
+	 * @since 5.2.2
+	 */
+	fun asyncDispatch(): ResultActionsDsl {
+		return andExpect {
+			request { asyncStarted() }
+		}.andReturn().let {
+			ResultActionsDsl(mockMvc.perform(MockMvcRequestBuilders.asyncDispatch(it)), mockMvc)
+		}
+	}
+
 	/**
 	 * @see ResultActions.andReturn
 	 */

spring-test/src/test/kotlin/org/springframework/test/web/servlet/MockMvcExtensionsTests.kt

@@ -25,6 +25,7 @@ import org.springframework.http.MediaType.*
 import org.springframework.test.web.Person
 import org.springframework.test.web.servlet.setup.MockMvcBuilders
 import org.springframework.web.bind.annotation.*
+import reactor.core.publisher.Mono
 import java.security.Principal
 import java.util.*
 
@@ -153,6 +154,13 @@ class MockMvcExtensionsTests {
 		}
 	}
 
+	@Test
+	fun asyncDispatch() {
+		mockMvc.get("/async").asyncDispatch().andExpect {
+			status { isOk }
+		}
+	}
+
 
 	@RestController
 	private class PersonController {
@@ -166,5 +174,10 @@ class MockMvcExtensionsTests {
 		@PostMapping("/person")
 		@ResponseStatus(HttpStatus.CREATED)
 		fun post(@RequestBody person: Person) {}
+
+		@GetMapping("/async")
+		fun getAsync(): Mono<Person> {
+			return Mono.just(Person("foo"))
+		}
 	}
 }