Polish Eager Header Config Tests

In the Java config tests, there is a simplified way to configure
Spring, and that is with SpringTestRule.

Also, test names typically follow the when-then convention.

Issue: gh-6501

Author: jzheaux

config/src/test/java/org/springframework/security/config/annotation/authentication/configurers/HeadersConfigurerJavaTests.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2002-2019 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.security.config.annotation.web.configurers;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.security.config.annotation.ObjectPostProcessor;
+import org.springframework.security.config.annotation.web.builders.HttpSecurity;
+import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
+import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
+import org.springframework.security.config.test.SpringTestRule;
+import org.springframework.security.web.header.HeaderWriterFilter;
+import org.springframework.test.web.servlet.MockMvc;
+
+import static org.springframework.http.HttpHeaders.*;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.header;
+
+/**
+ * Tests for {@link HeadersConfigurer}.
+ *
+ * @author Ankur Pathak
+ */
+public class HeadersConfigurerEagerHeadersTests {
+
+	@Rule
+	public final SpringTestRule spring = new SpringTestRule();
+
+	@Autowired
+	MockMvc mvc;
+
+	@EnableWebSecurity
+	public static class HeadersAtTheBeginningOfRequestConfig extends WebSecurityConfigurerAdapter {
+		@Override
+		protected void configure(HttpSecurity http) throws Exception {
+			//@ formatter:off
+			http
+				.headers()
+					.addObjectPostProcessor(new ObjectPostProcessor<HeaderWriterFilter>() {
+						@Override
+						public HeaderWriterFilter postProcess(HeaderWriterFilter filter) {
+							filter.setShouldWriteHeadersEagerly(true);
+							return filter;
+						}
+					});
+			//@ formatter:on
+		}
+	}
+
+	@Test
+	public void requestWhenHeadersEagerlyConfiguredThenHeadersAreWritten() throws Exception {
+		this.spring.register(HeadersAtTheBeginningOfRequestConfig.class).autowire();
+
+		this.mvc.perform(get("/").secure(true))
+				.andExpect(header().string("X-Content-Type-Options", "nosniff"))
+				.andExpect(header().string("X-Frame-Options", "DENY"))
+				.andExpect(header().string("Strict-Transport-Security", "max-age=31536000 ; includeSubDomains"))
+				.andExpect(header().string(CACHE_CONTROL, "no-cache, no-store, max-age=0, must-revalidate"))
+				.andExpect(header().string(EXPIRES, "0"))
+				.andExpect(header().string(PRAGMA, "no-cache"))
+				.andExpect(header().string("X-XSS-Protection", "1; mode=block"));
+	}
+}