QUnit test with promise

test.js

QUnit.test( 'checking bad reference', function ( assert ) {                                                                             
  assert.expect(1);
  return this.referencesGateway.getReference( '#cite_note-bad', this.page ).catch( function ( err ) {
    assert.ok( err === ReferencesGateway.ERROR_NOT_EXIST, 'When bad id given false returned.' );
    return null;
  } );
} );