Consume the http response to avoid IO exception

src/test/java/net/sourceforge/plantuml/servlet/TestImage.java

@@ -57,6 +57,10 @@ public class TestImage extends WebappTestCase {
         SimpleDateFormat format = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss ZZZ", Locale.ENGLISH);
         Date lastModified = format.parse( response.getHeaderField( "Last-Modified"));
         assertTrue( "Last-Modified is not in the past", lastModified.before( new Date()));
-        Thread.sleep(500); // Time to receive the image
+        // Consume the response
+        InputStream responseStream = response.getInputStream();
+        while( responseStream.read() != -1) {
+            ; // Do nothing
+        }
     }
 }