Mock a no-op promise.

mockPromise.js

/*
Needed to mock a promise for a test just so that chaining `then`s
and `catch`es wouldn't throw an error.  The actual execution of
those `then`s and `catches` could be no-ops since the test wasn't
concerned with their functionality.

The mocked promise (`returnMockThenable()`) was returned from a mock
`fetch` call.
*/

const returnMockThenable = () => ({
    then: returnMockThenable,
    catch: returnMockThenable,
});