SuggestedSyntax.java

@RegisterExtension
static ServerExtension server = ...;

@Test
void testRestApi() {
    WebTestClient client = server.webTestClient();
    client.get("/api/v1/carts")
          .execute()
          .assertStatus().isEqualTo(HttpStatus.OK) // or `isOk()` as an alias
          .assertHeaders().contain(HttpHeaderNames.CONTENT_TYPE, MediaType.JSON)
          .assertBody().contain(...)
          .assertTrailers().isEqualTo(Map.of(...));
}