DateRangeFieldComponent test triggers warning

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Bug Report or Feature Request (mark with an x)

- [x] bug report -> please search issues before submitting
- [ ] feature request

OS and Version?

Linux Ubuntu 18.04

Versions

npm: '6.4.1',

Repro steps

On ng-xform folder run:

npm test

The log given by the failure

WARN: 
    It looks like you're using ngModel on the same form field as formControlName.
    Support for using the ngModel input property and ngModelChange event with
    reactive form directives has been deprecated in Angular v6 and will be removed
    in Angular v7.

    For more information on this, see our API docs here:
    https://angular.io/api/forms/FormControlName#use-with-ngmodel