Frontend unit component testing for RecommendationStack.vue

[simaoalicechen]

This is not a priority, because it requires drag and drop testing.

Acceptance criteria

Created unit tests for components in RecommendationStack.vue
Pass as many tests as possible
Notify the contribution/reviewers about tests that cannot be passed

Definition of Done:
Pass as many tests as possible
Comment and move tests that cannot be passed for the nest sprints

[simaoalicechen]

1. Added 4 UI component tests;
2. Left comments and room for later API tests

Tests created: 4
Tests passed: 4