Write unit tests for Vuex store

[Venefilyn]

Current Vuex store is not tested and could use unit tests. Plenty of guides exists online for testing Vuex.

• [x] Create tests for actions
• [x] Create tests for getters
• [x] Create tests for mutations

Create tests for RoleSelector

• [x] Actions
• [x] Getters
• [x] Mutations