Testing Reactive Spring webflux using WebTestClient application context

Question

I am trying to test the following spring webflux Kotlin application with the WebTestClient and Junit 5:

@SpringBootApplication
class ReactiveKataApplication

fun main(args: Array<String>) {
    SpringApplicationBuilder(ReactiveKataApplication::class.java)
            .initializers(
                beans {
                    bean {
                        router {
                            GET("/frp/hello") {
                                ServerResponse.ok().body(Mono.just("Hello"), String::class.java)
                            }
                        }
                    }
            })
            .build()
            .run(*args)
}

I have the following test which is failing with a 404, can anyone help me identify the issue?

@TestInstance(TestInstance.Lifecycle.PER_CLASS)
@SpringBootTest
class ReactiveKataApplicationContextTest {

    private lateinit var webTestClient : WebTestClient

    @Autowired
    lateinit var context: ApplicationContext

    @BeforeAll
    fun initClient() {
        webTestClient = WebTestClient
                .bindToApplicationContext(context)
                .configureClient()
                .build()
    }

    @Test
    fun `calling hello world endpoint returns 200`() {
        webTestClient.get().uri("/frp/hello")
                .exchange()
                .expectStatus().isOk
    }

}

In the test log I see that the context is the ReactiveKataApplicationContextTest rather than the actual application, can anyone assist in resolving this using the WebTestClient binding to the Application Context?

2020-01-29 12:01:27.538  INFO 16269 --- [           main] c.o.r.ReactiveKataApplicationContextTest : Started ReactiveKataApplicationContextTest in 1.666 seconds (JVM running for 3.157)

I have tried @SpringBootTest(classes = [ ReactiveKataApplication::class ]) to no avail.

Git repo here: https://github.com/stefan-cross/reactive-spring-kata