public function testExtraFieldsViaExtension()
{
// This extends ManyManyListTest_Secondary with the secondary extension that adds the relationship back
// to the primary. The instance from the fixture is ManyManyListTest_SecondarySub, deliberately a sub-class of
// the extended class.
Object::add_extension('ManyManyListTest_Secondary', 'ManyManyListTest_IndirectSecondaryExtension');
// Test from the primary (not extended) to the secondary (which is extended)
$primary = $this->objFromFixture('ManyManyListTest_IndirectPrimary', 'manymany_extra_primary');
$secondaries = $primary->Secondary();
$extraFields = $secondaries->getExtraFields();
$this->assertTrue(count($extraFields) > 0, 'has extra fields');
$this->assertTrue(isset($extraFields['DocumentSort']), 'has DocumentSort');
// Test from the secondary (which is extended) to the primary (not extended)
$secondary = $this->objFromFixture('ManyManyListTest_SecondarySub', 'manymany_extra_secondary');
$primaries = $secondary->Primary();
$extraFields = $primaries->getExtraFields();
$this->assertTrue(count($extraFields) > 0, 'has extra fields');
$this->assertTrue(isset($extraFields['DocumentSort']), 'has DocumentSort');
}