WIP: Add tests on search multiple

...pp/instance/store/effects/search-multiple.effects.spec.ts

...src/app/instance/store/effects/search-multiple.effects.ts

client/src/app/instance/store/models/criterion.model.ts

...store/models/criterion/select-multiple-criterion.model.ts

...app/instance/store/models/search-multiple-dataset-data.ts

...p/instance/store/models/search-multiple-dataset-length.ts

...p/instance/store/reducers/search-multiple.reducer.spec.ts

...rc/app/instance/store/reducers/search-multiple.reducer.ts

...instance/store/selectors/search-multiple.selector.spec.ts