Clear MethodsV2 cache on engine reset

A previous commit introduced memoization of one particular function in
MethodsV2. Make sure we can invalidate the cache, and make sure it
happens when calling Zonemaster::Engine::reset().

Author: marc-vanderwal

lib/Zonemaster/Engine.pm

@@ -231,6 +231,7 @@ sub reset {
     Zonemaster::Engine::Nameserver->empty_cache();
     $logger->clear_history() if $logger;
     Zonemaster::Engine::Recursor->clear_cache();
+    Zonemaster::Engine::TestMethodsV2->clear_cache();
     return;
 }
 
@@ -408,7 +409,8 @@ Set the logger's start time to the current time.
 =item reset()
 
 Reset logger start time to current time, empty the list of log messages, clear
-nameserver object cache and recursor cache.
+nameserver object cache, clear recursor cache and clear all cached results of
+MethodsV2.
 
 =back
 

lib/Zonemaster/Engine/TestMethodsV2.pm

@@ -36,6 +36,8 @@ Takes a L<Zonemaster::Engine::Zone> object.
 
 Returns an arrayref of L<Zonemaster::Engine::Nameserver> objects, or C<undef> if no parent zone was found.
 
+The result of this Method is cached for performance reasons. This cache can be invalidated by calling C<clear_cache()> if necessary.
+
 =back
 
 =cut
@@ -786,4 +788,19 @@ sub get_zone_ns_ips {
     return [ uniq sort @ns_ips ];
 }
 
+
+=over
+
+=item clear_cache()
+
+Clears previously cached results of the C<get_parent_ns_ips()> method.
+
+=back
+
+=cut
+
+sub clear_cache() {
+    Memoize::flush_cache(\&get_parent_ns_ips);
+}
+
 1;