> I think I got your proposal but sadly there is a problem this it since in the tests cases we are not using the real l10 but a mock. More concretely https://github.com/mozilla-b2g/gaia/blob/master/shared/test/unit/mocks/dialer/mock_lazy_l10n.js which as you will see does no real localization work :(

Yeah, you're right. However, if we implement my above suggestion where we check for the presence of a number instead of the ```:``` character, we can write this as:
```js
var totalCallDuration = _('totalDurationMinutes', 1234);
```
This test should then pass since the outputted string will look something like:
```
totalDurationMinutes{1234}
```