Add bindToHttpHandler to WebTestClient

Issue: SPR-15499

spring-test/src/test/java/org/springframework/test/web/reactive/server/samples/bind/HttpHandlerTests.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2002-2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.test.web.reactive.server.samples.bind;
+
+import java.nio.charset.StandardCharsets;
+import java.util.Collections;
+
+import org.junit.Test;
+import reactor.core.publisher.Mono;
+
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DefaultDataBufferFactory;
+import org.springframework.http.server.reactive.HttpHandler;
+import org.springframework.test.web.reactive.server.WebTestClient;
+import org.springframework.web.server.WebFilter;
+import org.springframework.web.server.adapter.WebHttpHandlerBuilder;
+
+/**
+ * Bind to an {@link HttpHandler}.
+ * @author Rossen Stoyanchev
+ */
+public class HttpHandlerTests {
+
+
+	@Test
+	public void testWebFilter() throws Exception {
+
+		WebFilter myFilter = (exchange, chain) -> {
+			DataBuffer buffer = new DefaultDataBufferFactory().allocateBuffer();
+			buffer.write("It works!".getBytes(StandardCharsets.UTF_8));
+			return exchange.getResponse().writeWith(Mono.just(buffer));
+		};
+
+		HttpHandler httpHandler = WebHttpHandlerBuilder.webHandler(exchange -> Mono.empty())
+				.filters(Collections.singletonList(myFilter)).build();
+
+		WebTestClient.bindToHttpHandler(httpHandler).build()
+				.get().uri("/")
+				.exchange()
+				.expectStatus().isOk()
+				.expectBody(String.class).isEqualTo("It works!");
+	}
+
+}