Provide XML assertions in WebTestClient

Adds XML-based assertions in
org.springframework.test.web.reactive.server.WebTestClient.BodyContentSpec
for asserting against the XML body as well as xPath,
similar to those assertions offered when using
MockMvcResultMatchers.xpath().

Issue: SPR-16741

spring-test/src/main/java/org/springframework/test/web/reactive/server/DefaultWebTestClient.java

@@ -27,6 +27,7 @@ import java.util.Optional;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.function.Consumer;
 import java.util.function.Function;
+import javax.xml.xpath.XPathExpressionException;
 
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
@@ -40,6 +41,7 @@ import org.springframework.http.client.reactive.ClientHttpConnector;
 import org.springframework.http.client.reactive.ClientHttpRequest;
 import org.springframework.lang.Nullable;
 import org.springframework.test.util.JsonExpectationsHelper;
+import org.springframework.test.util.XmlExpectationsHelper;
 import org.springframework.util.Assert;
 import org.springframework.util.MimeType;
 import org.springframework.util.MultiValueMap;
@@ -476,11 +478,34 @@ class DefaultWebTestClient implements WebTestClient {
 			return this;
 		}
 
+		@Override
+		public BodyContentSpec xml(String expectedXml) {
+			this.result.assertWithDiagnostics(() -> {
+				try {
+					new XmlExpectationsHelper().assertXmlEqual(expectedXml, getBodyAsString());
+				}
+				catch (Exception ex) {
+					throw new AssertionError("XML parsing error", ex);
+				}
+			});
+			return this;
+		}
+
 		@Override
 		public JsonPathAssertions jsonPath(String expression, Object... args) {
 			return new JsonPathAssertions(this, getBodyAsString(), expression, args);
 		}
 
+		@Override
+		public XpathAssertions xpath(String expression, Map<String, String> namespaces, Object... args) {
+			try {
+				return new XpathAssertions(this, expression, namespaces, args);
+			}
+			catch (XPathExpressionException ex) {
+				throw new AssertionError("XML parsing error", ex);
+			}
+		}
+
 		private String getBodyAsString() {
 			byte[] body = this.result.getResponseBody();
 			if (body == null || body.length == 0) {

spring-test/src/main/java/org/springframework/test/web/reactive/server/WebTestClient.java

@@ -819,6 +819,14 @@ public interface WebTestClient {
 		 */
 		BodyContentSpec json(String expectedJson);
 
+		/**
+		 * Parse the expected and actual response content as XML and perform a
+		 * comparison verifying the same structure.
+		 * @param expectedXml the expected JSON content.
+		 * @since 5.1
+		 */
+		BodyContentSpec xml(String expectedXml);
+
 		/**
 		 * Access to response body assertions using a
 		 * <a href="https://github.com/jayway/JsonPath">JsonPath</a> expression
@@ -830,6 +838,32 @@ public interface WebTestClient {
 		 */
 		JsonPathAssertions jsonPath(String expression, Object... args);
 
+		/**
+		 * Access to response body assertions using an XPath expression to inspect a specific
+		 * subset of the body.
+		 * <p>The XPath expression can be a parameterized string using
+		 * formatting specifiers as defined in {@link String#format}.
+		 * @param expression The XPath expression
+		 * @param args arguments to parameterize the expression
+		 * @see #xpath(String, Map, Object...)
+		 * @since 5.1
+		 */
+		default XpathAssertions xpath(String expression, Object... args){
+			return xpath(expression, null, args);
+		}
+
+		/**
+		 * Access to response body assertions with specific namespaces using an XPath
+		 * expression to inspect a specific subset of the body.
+		 * <p>The XPath expression can be a parameterized string using
+		 * formatting specifiers as defined in {@link String#format}.
+		 * @param expression The XPath expression
+		 * @param namespaces The namespaces
+		 * @param args arguments to parameterize the expression
+		 * @since 5.1
+		 */
+		XpathAssertions xpath(String expression, Map<String, String> namespaces, Object... args);
+
 		/**
 		 * Assert the response body content with the given {@link Consumer}.
 		 * @param consumer the consumer for the response body; the input

spring-test/src/main/java/org/springframework/test/web/reactive/server/XpathAssertions.java

@@ -0,0 +1,159 @@
+/*
+ * Copyright 2002-2018 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;
+
+import java.nio.charset.StandardCharsets;
+import java.util.Map;
+import java.util.Optional;
+import javax.xml.xpath.XPathExpressionException;
+
+import org.hamcrest.Matcher;
+import org.w3c.dom.Node;
+
+import org.springframework.http.HttpHeaders;
+import org.springframework.lang.Nullable;
+import org.springframework.test.util.XpathExpectationsHelper;
+import org.springframework.util.MimeType;
+
+/**
+ * XPath assertions for a {@link WebTestClient}.
+ *
+ * @author Eric Deandrea
+ * @since 5.1
+ */
+public class XpathAssertions {
+
+	private final WebTestClient.BodyContentSpec bodySpec;
+
+	private final XpathExpectationsHelper xpathHelper;
+
+	XpathAssertions(WebTestClient.BodyContentSpec spec, String expression, @Nullable Map<String, String> namespaces, Object... args) throws XPathExpressionException {
+		this.bodySpec = spec;
+		this.xpathHelper = new XpathExpectationsHelper(expression, namespaces, args);
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper#assertString(byte[], String, String)}
+	 */
+	public WebTestClient.BodyContentSpec isEqualTo(String expectedValue) {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.assertString(getResponseBody(), getDefinedEncoding(), expectedValue));
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper#assertNumber(byte[], String, Double)}
+	 */
+	public WebTestClient.BodyContentSpec isEqualTo(Double expectedValue) {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.assertNumber(getResponseBody(), getDefinedEncoding(), expectedValue));
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper#assertBoolean(byte[], String, boolean)}
+	 */
+	public WebTestClient.BodyContentSpec isEqualTo(boolean expectedValue) {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.assertBoolean(getResponseBody(), getDefinedEncoding(), expectedValue));
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper#exists(byte[], String)}
+	 */
+	public WebTestClient.BodyContentSpec exists() {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.exists(getResponseBody(), getDefinedEncoding()));
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper#doesNotExist(byte[], String)}
+	 */
+	public WebTestClient.BodyContentSpec doesNotExist() {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.doesNotExist(getResponseBody(), getDefinedEncoding()));
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper[#assertNodeCount(byte[], String, int)}
+	 */
+	public WebTestClient.BodyContentSpec nodeCount(int expectedCount) {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.assertNodeCount(getResponseBody(), getDefinedEncoding(), expectedCount));
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper#assertNodeCount(byte[], String, Matcher)}
+	 */
+	public WebTestClient.BodyContentSpec nodeCount(Matcher<Integer> matcher) {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.assertNodeCount(getResponseBody(), getDefinedEncoding(), matcher));
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper#assertNode(byte[], String, Matcher)}
+	 */
+	public WebTestClient.BodyContentSpec nodeMatches(Matcher<? super Node> matcher) {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.assertNode(getResponseBody(), getDefinedEncoding(), matcher));
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper#assertString(byte[], String, Matcher)}
+	 */
+	public WebTestClient.BodyContentSpec matchesString(Matcher<? super String> matcher) {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.assertString(getResponseBody(), getDefinedEncoding(), matcher));
+	}
+
+	/**
+	 * Applies {@link XpathExpectationsHelper#assertNumber(byte[], String, Matcher)}
+	 */
+	public WebTestClient.BodyContentSpec matchesNumber(Matcher<? super Double> matcher) {
+		return performXmlAssertionAndHandleError(() -> this.xpathHelper.assertNumber(getResponseBody(), getDefinedEncoding(), matcher));
+	}
+
+	private WebTestClient.BodyContentSpec performXmlAssertionAndHandleError(AssertionThrowingRunnable assertion) {
+		assertion.run();
+		return this.bodySpec;
+	}
+
+	private byte[] getResponseBody() {
+		return getResult().getResponseBody();
+	}
+
+	private EntityExchangeResult<byte[]> getResult() {
+		return this.bodySpec.returnResult();
+	}
+
+	private String getDefinedEncoding() {
+		return Optional.ofNullable(getResult())
+				.map(EntityExchangeResult::getResponseHeaders)
+				.map(HttpHeaders::getContentType)
+				.map(MimeType::getCharset)
+				.orElse(StandardCharsets.UTF_8)
+				.name();
+	}
+
+	/**
+	 * Lets us be able to use lambda expressions that could throw checked exceptions, since
+	 * {@link XpathExpectationsHelper} throws {@link Exception} on its methods.
+	 */
+	@FunctionalInterface
+	private interface AssertionThrowingRunnable extends Runnable {
+		void runThrows() throws Exception;
+
+		@Override
+		default void run() {
+			try {
+				runThrows();
+			}
+			catch (Exception ex) {
+				throw new AssertionError("XML parsing error", ex);
+			}
+		}
+	}
+}