Lenient date parsing in HeadersResultMatchers

Rather than formatting the expected value, and be susceptible to
minor formatting differences (e.g. 01 vs 1 for day of month), parse the
actual header value leniently with HttpHeaders and compare time values.

Issue: SPR-17330

spring-test/src/test/java/org/springframework/test/web/servlet/result/HeaderResultMatchersTests.java

@@ -0,0 +1,54 @@
+/*
+ * 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.servlet.result;
+
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+
+import org.junit.Test;
+
+import org.springframework.http.HttpHeaders;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockHttpServletResponse;
+import org.springframework.test.web.servlet.MvcResult;
+import org.springframework.test.web.servlet.StubMvcResult;
+
+/**
+ * Unit tests for {@link HeaderResultMatchers}.
+ * @author Rossen Stoyanchev
+ */
+public class HeaderResultMatchersTests {
+
+	private final HeaderResultMatchers matchers = new HeaderResultMatchers();
+
+	private final MockHttpServletResponse response = new MockHttpServletResponse();
+
+	private final MvcResult mvcResult =
+			new StubMvcResult(new MockHttpServletRequest(), null, null, null, null, null, this.response);
+
+
+	@Test // SPR-17330
+	public void matchDateFormattedWithHttpHeaders() throws Exception {
+
+		long epochMilli = ZonedDateTime.of(2018, 10, 5, 0, 0, 0, 0, ZoneId.of("GMT")).toInstant().toEpochMilli();
+		HttpHeaders headers = new HttpHeaders();
+		headers.setDate("myDate", epochMilli);
+		this.response.setHeader("d", headers.getFirst("myDate"));
+
+		this.matchers.dateValue("d", epochMilli).match(this.mvcResult);
+	}
+
+}

spring-test/src/test/java/org/springframework/test/web/servlet/samples/standalone/resultmatchers/HeaderAssertionTests.java

@@ -208,7 +208,8 @@ public class HeaderAssertionTests {
 
 	private void assertMessageContains(AssertionError error, String expected) {
 		String message = error.getMessage();
-		assertTrue("Failure message should contain: " + expected, message.contains(expected));
+		assertTrue("Failure message should contain [" + expected + "], actual is [" + message + "]",
+				message.contains(expected));
 	}