@mixin foo($custom: ()) {
  $foo: create-config((
    'foo' : ('bar' : false)
  ), $custom);
}

@include test-module('this') {
  @include test('get a value from the current module`s configuration') {
    @include foo((
      'foo' : ('bar' : true)
    ));

    $actual: this('foo', 'bar');
    $expected: true;

    @include assert-equal($actual, $expected, 'should return the expected value');
  }
}