Add test to ensure ForwardedHeaderFilter contextPath preserves encoding

Add a test to verify that the ForwardedHeaderFilter contextPath override preserves URL encoding
as it should.

Issue SPR-15422

spring-web/src/test/java/org/springframework/web/filter/ForwardedHeaderFilterTests.java

@@ -245,6 +245,17 @@ public class ForwardedHeaderFilterTests {
 		assertEquals("/prefix", actual);
 	}
 
+	@Test
+	public void contextPathPreserveEncoding() throws Exception {
+		this.request.setContextPath("/app%20");
+		this.request.setRequestURI("/app%20/path/");
+		HttpServletRequest actual = filterAndGetWrappedRequest();
+
+		assertEquals("/app%20", actual.getContextPath());
+		assertEquals("/app%20/path/", actual.getRequestURI());
+		assertEquals("http://localhost/app%20/path/", actual.getRequestURL().toString());
+	}
+
 	@Test
 	public void sendRedirectWithAbsolutePath() throws Exception {
 		this.request.addHeader(X_FORWARDED_PROTO, "https");