How to call MockFirebase.override()

[Dashing-Daniel-Li]

I keep getting this error:
TypeError: __WEBPACK_IMPORTED_MODULE_1_mockfirebase___default.a.override is not a function

In my spec.ts I imported it at the top

import MockFirebase from'mockfirebase';

then in my before each i called:
MockFirebase.override();

Does it need to be in the karma config and where ??
I am making an ionic app using ionic example testing git repo.

[Dashing-Daniel-Li]

var MockFirebase = require('mockfirebase').MockFirebase;

in the setup instructions where do i put this?