#320 improve duplicate interfaces() fixup

1. sorts the interfaces as they are processed to make A/B testing easier
2. adds the interface index to the original when a duplicate is seen
3. there may be other de-duplication code in vendor modules, untouched

xt/lib/Test/SNMP/Info/Layer3.pm

@@ -47,9 +47,33 @@ sub setup : Tests(setup) {
 
   # Start with a common cache that will serve most tests
   my $cache_data = {
-    'store' => {},
+    '_i_index' => 1,
+    '_i_description' => 1,
+    'store' => {
+      'i_index' => {1 => 1, 2 => 2, 3 => 3, 4 => 4},
+      'i_description' => {
+        1 => 'Unique Interface Name',
+        2 => 'Duplicate Interface Name',
+        3 => 'Duplicate Interface Name'
+      },
+    },
   };
   $test->{info}->cache($cache_data);
 }
 
+sub duplicates : Tests(2) {
+  my $test = shift;
+
+  my $expected_data = {
+    1 => 'Unique Interface Name',
+    2 => 'Duplicate Interface Name (2)',
+    3 => 'Duplicate Interface Name (3)',
+    4 => 4,
+  };
+
+  can_ok($test->{info}, 'interfaces');
+  cmp_deeply($test->{info}->interfaces(),
+    $expected_data, 'Call to interfaces() removes duplicates');
+}
+
 1;