WIP: Add tests

Finish creating tests for the frontend as part of https://gitlab.com/LibreFoodPantry/modules/visitmodule-tp/updateguest/Plan/-/issues/41.

Sources used:

• https://medium.com/@kevinkreuzer/test-your-components-using-angular-materials-component-harnesses-f9c1deebdf5d
• https://material.angular.io/cdk/test-harnesses/overview
• https://material.angular.io/guide/using-component-harnesses