Extracted removeUserFromCache(String) to UserCache interface.

core/src/test/java/org/acegisecurity/providers/dao/DaoAuthenticationProviderTests.java

@@ -354,5 +354,7 @@ public class DaoAuthenticationProviderTests extends TestCase {
         public void putUserInCache(UserDetails user) {
             cache.put(user.getUsername(), user);
         }
+
+        public void removeUserFromCache(String username) {}
     }
 }

core/src/test/java/org/acegisecurity/providers/dao/cache/NullUserCacheTests.java

@@ -53,6 +53,7 @@ public class NullUserCacheTests extends TestCase {
         NullUserCache cache = new NullUserCache();
         cache.putUserInCache(getUser());
         assertNull(cache.getUserFromCache(null));
+        cache.removeUserFromCache(null);
     }
 
     private User getUser() {