Add AssertJ support for MockMvc

Closes gh-21178

spring-test/spring-test.gradle

@@ -32,6 +32,7 @@ dependencies {
 	optional("org.apache.groovy:groovy")
 	optional("org.apache.tomcat.embed:tomcat-embed-core")
 	optional("org.aspectj:aspectjweaver")
+	optional("org.assertj:assertj-core")
 	optional("org.hamcrest:hamcrest")
 	optional("org.htmlunit:htmlunit") {
 		exclude group: "commons-logging", module: "commons-logging"

spring-test/src/main/java/org/springframework/test/http/HttpHeadersAssert.java

@@ -0,0 +1,129 @@
+/*
+ * Copyright 2002-2024 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
+ *
+ *      https://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.http;
+
+import java.time.Instant;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.time.temporal.ChronoUnit;
+import java.util.List;
+
+import org.assertj.core.api.AbstractMapAssert;
+import org.assertj.core.api.Assertions;
+
+import org.springframework.http.HttpHeaders;
+
+/**
+ * AssertJ {@link org.assertj.core.api.Assert assertions} that can be applied to
+ * {@link HttpHeaders}.
+ *
+ * @author Stephane Nicoll
+ * @since 6.2
+ */
+public class HttpHeadersAssert extends AbstractMapAssert<HttpHeadersAssert, HttpHeaders, String, List<String>> {
+
+	private static final ZoneId GMT = ZoneId.of("GMT");
+
+
+	public HttpHeadersAssert(HttpHeaders actual) {
+		super(actual, HttpHeadersAssert.class);
+		as("HTTP headers");
+	}
+
+	/**
+	 * Verify that the actual HTTP headers contain a header with the given
+	 * {@code name}.
+	 * @param name the name of an expected HTTP header
+	 * @see #containsKey
+	 */
+	public HttpHeadersAssert containsHeader(String name) {
+		return containsKey(name);
+	}
+
+	/**
+	 * Verify that the actual HTTP headers contain the headers with the given
+	 * {@code names}.
+	 * @param names the names of expected HTTP headers
+	 * @see #containsKeys
+	 */
+	public HttpHeadersAssert containsHeaders(String... names) {
+		return containsKeys(names);
+	}
+
+	/**
+	 * Verify that the actual HTTP headers do not contain a header with the
+	 * given {@code name}.
+	 * @param name the name of an HTTP header that should not be present
+	 * @see #doesNotContainKey
+	 */
+	public HttpHeadersAssert doesNotContainsHeader(String name) {
+		return doesNotContainKey(name);
+	}
+
+	/**
+	 * Verify that the actual HTTP headers do not contain any of the headers
+	 * with the given {@code names}.
+	 * @param names the names of HTTP headers that should not be present
+	 * @see #doesNotContainKeys
+	 */
+	public HttpHeadersAssert doesNotContainsHeaders(String... names) {
+		return doesNotContainKeys(names);
+	}
+
+	/**
+	 * Verify that the actual HTTP headers contain a header with the given
+	 * {@code name} and {@link String} {@code value}.
+	 * @param name the name of the cookie
+	 * @param value the expected value of the header
+	 */
+	public HttpHeadersAssert hasValue(String name, String value) {
+		containsKey(name);
+		Assertions.assertThat(this.actual.getFirst(name))
+				.as("check primary value for HTTP header '%s'", name)
+				.isEqualTo(value);
+		return this.myself;
+	}
+
+	/**
+	 * Verify that the actual HTTP headers contain a header with the given
+	 * {@code name} and {@link Long} {@code value}.
+	 * @param name the name of the cookie
+	 * @param value the expected value of the header
+	 */
+	public HttpHeadersAssert hasValue(String name, long value) {
+		containsKey(name);
+		Assertions.assertThat(this.actual.getFirst(name))
+				.as("check primary long value for HTTP header '%s'", name)
+				.asLong().isEqualTo(value);
+		return this.myself;
+	}
+
+	/**
+	 * Verify that the actual HTTP headers contain a header with the given
+	 * {@code name} and {@link Instant} {@code value}.
+	 * @param name the name of the cookie
+	 * @param value the expected value of the header
+	 */
+	public HttpHeadersAssert hasValue(String name, Instant value) {
+		containsKey(name);
+		Assertions.assertThat(this.actual.getFirstZonedDateTime(name))
+				.as("check primary date value for HTTP header '%s'", name)
+				.isCloseTo(ZonedDateTime.ofInstant(value, GMT), Assertions.within(999, ChronoUnit.MILLIS));
+		return this.myself;
+	}
+
+}

spring-test/src/main/java/org/springframework/test/http/MediaTypeAssert.java

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2002-2024 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
+ *
+ *      https://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.http;
+
+import org.assertj.core.api.AbstractObjectAssert;
+import org.assertj.core.api.Assertions;
+import org.assertj.core.error.BasicErrorMessageFactory;
+import org.assertj.core.internal.Failures;
+
+import org.springframework.http.InvalidMediaTypeException;
+import org.springframework.http.MediaType;
+import org.springframework.lang.Nullable;
+import org.springframework.util.StringUtils;
+
+/**
+ * AssertJ {@link org.assertj.core.api.Assert assertions} that can be applied
+ * to a {@link MediaType}.
+ *
+ * @author Brian Clozel
+ * @author Stephane Nicoll
+ * @since 6.2
+ */
+public class MediaTypeAssert extends AbstractObjectAssert<MediaTypeAssert, MediaType> {
+
+	public MediaTypeAssert(@Nullable MediaType mediaType) {
+		super(mediaType, MediaTypeAssert.class);
+		as("Media type");
+	}
+
+	public MediaTypeAssert(@Nullable String actual) {
+		this(StringUtils.hasText(actual) ? MediaType.parseMediaType(actual) : null);
+	}
+
+	/**
+	 * Verify that the actual media type is equal to the given string
+	 * representation.
+	 * @param expected the expected media type
+	 */
+	public MediaTypeAssert isEqualTo(String expected) {
+		return isEqualTo(parseMediaType(expected));
+	}
+
+	/**
+	 * Verify that the actual media type is
+	 * {@linkplain MediaType#isCompatibleWith(MediaType) compatible} with the
+	 * given one. Example: <pre><code class='java'>
+	 * // Check that actual is compatible with "application/json"
+	 * assertThat(mediaType).isCompatibleWith(MediaType.APPLICATION_JSON);
+	 * </code></pre>
+	 * @param mediaType the media type with which to compare
+	 */
+	public MediaTypeAssert isCompatibleWith(MediaType mediaType) {
+		Assertions.assertThat(this.actual)
+				.withFailMessage("Expecting null to be compatible with '%s'", mediaType).isNotNull();
+		Assertions.assertThat(mediaType)
+				.withFailMessage("Expecting '%s' to be compatible with null", this.actual).isNotNull();
+		Assertions.assertThat(this.actual.isCompatibleWith(mediaType))
+				.as("check media type '%s' is compatible with '%s'", this.actual.toString(), mediaType.toString())
+				.isTrue();
+		return this;
+	}
+
+	/**
+	 * Verify that the actual media type is
+	 * {@linkplain MediaType#isCompatibleWith(MediaType) compatible} with the
+	 * given one. Example: <pre><code class='java'>
+	 * // Check that actual is compatible with "text/plain"
+	 * assertThat(mediaType).isCompatibleWith("text/plain");
+	 * </code></pre>
+	 * @param mediaType the media type with which to compare
+	 */
+	public MediaTypeAssert isCompatibleWith(String mediaType) {
+		return isCompatibleWith(parseMediaType(mediaType));
+	}
+
+
+	private MediaType parseMediaType(String value) {
+		try {
+			return MediaType.parseMediaType(value);
+		}
+		catch (InvalidMediaTypeException ex) {
+			throw Failures.instance().failure(this.info, new ShouldBeValidMediaType(value, ex.getMessage()));
+		}
+	}
+
+	private static final class ShouldBeValidMediaType extends BasicErrorMessageFactory {
+
+		private ShouldBeValidMediaType(String mediaType, String errorMessage) {
+			super("%nExpecting:%n  %s%nTo be a valid media type but got:%n  %s%n", mediaType, errorMessage);
+		}
+	}
+
+}

spring-test/src/main/java/org/springframework/test/http/package-info.java

@@ -0,0 +1,9 @@
+/**
+ * Test support for HTTP concepts.
+ */
+@NonNullApi
+@NonNullFields
+package org.springframework.test.http;
+
+import org.springframework.lang.NonNullApi;
+import org.springframework.lang.NonNullFields;