Make tests tolerate varying presence of Content-Length header

In Framework 5.2, the Content-Length is now provided by MockMvc. In
earlier versions it is not. This commit updates the tests to tolerate
this difference in behaviour so that the compatibility tests pass
again.

Author: wilkinsona

spring-restdocs-mockmvc/src/test/java/org/springframework/restdocs/mockmvc/MockMvcRestDocumentationIntegrationTests.java

@@ -25,8 +25,10 @@
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.regex.Pattern;
 
 import javax.servlet.http.Cookie;
@@ -385,11 +387,17 @@ public void preprocessedRequest() throws Exception {
 								replacePattern(pattern, "\"<<beta>>\""))))
 				.andReturn();
 		HttpRequestCondition originalRequest = httpRequest(TemplateFormats.asciidoctor(), RequestMethod.GET, "/");
+		Set<String> mvcResultHeaderNames = new HashSet<>();
 		for (String headerName : IterableEnumeration.of(result.getRequest().getHeaderNames())) {
 			originalRequest.header(headerName, result.getRequest().getHeader(headerName));
+			mvcResultHeaderNames.add(headerName);
 		}
-		assertThat(new File("build/generated-snippets/original-request/http-request.adoc")).has(content(originalRequest
-				.header("Host", "localhost:8080").header("Content-Length", "13").content("{\"a\":\"alpha\"}")));
+		originalRequest.header("Host", "localhost:8080");
+		if (!mvcResultHeaderNames.contains("Content-Length")) {
+			originalRequest.header("Content-Length", "13");
+		}
+		assertThat(new File("build/generated-snippets/original-request/http-request.adoc"))
+				.has(content(originalRequest.content("{\"a\":\"alpha\"}")));
 		HttpRequestCondition preprocessedRequest = httpRequest(TemplateFormats.asciidoctor(), RequestMethod.GET, "/");
 		List<String> removedHeaders = Arrays.asList("a", HttpHeaders.HOST, HttpHeaders.CONTENT_LENGTH);
 		for (String headerName : IterableEnumeration.of(result.getRequest().getHeaderNames())) {