Typesense backend needs tests #246
Description
The new Typesense backend was not originally planned to merge, and we were requested to develop it without tests for now.
It has been included without unit tests for now as the budget is tight, there is limited value in unit tests compared to integration tests, Typesense integration tests would be a bigger project, all the common edx-search functionality is already unit-tested, and Typesense support is still somewhat experimental.
However, we can and should add both unit and integration tests for the Typesense backend.
It may make sense to do this after or together with #245 (re-architecting this repo).