Mixpanel returning a response object instead of undefined even when opted out in AVA Unit Test

Question

I'm trying to implement an AVA Unit Test for my mixpanel implementation. To do this, I'm comparing the result of mixpanel.track() where if it returns anything, the track was successful, otherwise, it should be undefined.

I thought maybe it was that it was using a different mixpanel instance so I tried creating a named instance and ensuring that but it was to no avail. I'm also trying the same process but with Amplitude and it seems to be working fine (when I am opted out, the response fails as expected)

I have done this in my components where if const test = mixpanel.track('event_name', {}) is successful, !!test === true but if I do mixpanel.opt_out.tracking() prior to const test = mixpanel.track('event_name', {}), then !!test === undefined.

Expected behaviour (and the observed behaviour when I use it in my components):

trackResponse === undefined

Observed behaviour:

trackResponse === { event: 'asdf',
  properties:
   { '$browser': 'Safari',
     '$current_url': 'about:blank',
     '$browser_version': null,
     '$screen_height': 0,
     '$screen_width': 0,
     mp_lib: 'web',
     '$lib_version': '2.30.1',
     time: 1572898982.142,
     distinct_id: '[some_id]',
     '$device_id': '[some_id]',
     '$initial_referrer': '$direct',
     '$initial_referring_domain': '$direct',
     token: '[token]' } }

where [some_id] and [token] are some distinct values I've deleted.

I don't understand why in the AVA test, I'm receiving a response when normally a failed track() results in an undefined response. Could someone shine some light on this?

Let me know if I need to provide any additional information. Thanks.

Answer 1

I figured it out in case anyone else runs into this issue.

I used a debugger to step into the mixpanel.track() calls and figured out that to see if the user had opted out, mixpanel checks for a property in the localStorage and compares it to see if it's === to '0'. If this fails, it assumes the user has not opted out and carries out the track call as normal.

I guess during the AVA test, it was unable to access this property and assumed the user had not opted out. To fix it, in my call to mixpanel.init(), I added opt_out_tracking_persistence_type: 'cookie' as an option so that my opt_out call was being saved somewhere that the property could be accessed during the test.