Bug 28744: Regression tests

This patch adds tests for the following cases:
- to_api_mapping not defined
- to_api_mapping returning an empty hashref

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Object.t
=> FAIL: Tests fail :-(

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>

Signed-off-by: David Nind <david@davidnind.com>

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>

JD amended patch: remove uneeded commented lines

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

t/db_dependent/Koha/Object.t

@@ -390,7 +390,7 @@ subtest "to_api_mapping() tests" => sub {
 
 subtest "from_api_mapping() tests" => sub {
 
-    plan tests => 3;
+    plan tests => 5;
 
     $schema->storage->txn_begin;
 
@@ -449,6 +449,28 @@ subtest "from_api_mapping() tests" => sub {
         'Fresh mapping loaded'
     );
 
+    $city_class->unmock( 'to_api_mapping');
+    $city_class->mock( 'to_api_mapping', undef );
+
+    # Get a fresh object
+    $city = $builder->build_object({ class => 'Koha::Cities' });
+    is_deeply(
+        $city->from_api_mapping,
+        {},
+        'No to_api_mapping then empty hashref'
+    );
+
+    $city_class->unmock( 'to_api_mapping');
+    $city_class->mock( 'to_api_mapping', sub { return; } );
+
+    # Get a fresh object
+    $city = $builder->build_object({ class => 'Koha::Cities' });
+    is_deeply(
+        $city->from_api_mapping,
+        {},
+        'Empty to_api_mapping then empty hashref'
+    );
+
     $schema->storage->txn_rollback;
 };