I'm not able to mock async chronik calls that will later come in this function.

gating them with this flag and accepting mocks of known chronik responses is an effective way to test function logic without hitting the API

Alternatively, the unit test can hit the API.

Another issue that will be raised is creating / reading / writing to mongod. There are complicated modules available which mock this, but then we have a similar issue; unit test is testing a mock module and not the used database.

Available options imo are

1. Gate with isUnitTest variable to test function behavior at key logic junctures with templated API and mongod responses
2. Call the APIs + fire up a database before unit tests

In this case I'm just used to avoiding API calls in unit tests, hence the flag. But if we can do these in CI, might as well.

that would crash on app startup since wsMsg.blockHash is undefined