Service dependency issue with Angular 4.x

Skeleton project to reproduce the service dependency issue that i have.

Scenario

ContactService depends on SkillsService. When running ng test it outputs the following...

Error: No provider for SkillsService!

How do i configure it so that i have a SkillsService provider?

This project was generated with Angular CLI version 1.2.3.

Development server

Run ng serve for a dev server. Navigate to http://localhost:4200/. The app will automatically reload if you change any of the source files.

Code scaffolding

Run ng generate component component-name to generate a new component. You can also use ng generate directive|pipe|service|class|module.

Build

Run ng build to build the project. The build artifacts will be stored in the dist/ directory. Use the -prod flag for a production build.

Running unit tests

Run ng test to execute the unit tests via Karma.

Running end-to-end tests

Run ng e2e to execute the end-to-end tests via Protractor. Before running the tests make sure you are serving the app via ng serve.

Further help

To get more help on the Angular CLI use ng help or go check out the Angular CLI README.