Trigger a subscription-expired error mid-playback

MusicKit JS surfaces a subscription error from two body-driven endpoints — web-playback (the per-song playback payload) and the license-acquisition endpoints. Either path causes the page to see MKError.Reason.SUBSCRIPTION_ERROR; pick the one your code path actually exercises.

At the web-playback endpoint

from musickit_api_mock import (
    MusicKitApiMock,
    WebPlaybackResponseSubscriptionError,
)

mock = MusicKitApiMock()

mock.endpoints.web_playback = {
    "1000000001": WebPlaybackResponseSubscriptionError(),
}

The web-playback setter is keyed by salable adam id, so only the listed song triggers the error. Other ids resolve through whatever else is configured (or raise if unset).

At the license endpoint

from musickit_api_mock import (
    LicenseResponseSubscriptionError,
    MusicKitApiMock,
)

mock = MusicKitApiMock()

mock.endpoints.license_catalog_song = {
    "1000000001": LicenseResponseSubscriptionError(),
}

Use this when you want the playback metadata fetch to succeed and the failure to surface only when the CDM requests the license — closer to a "subscription lapsed between fetch and play" scenario.

Flip a healthy session into expired

Both setters accept a callable. Use a closure to start with success and switch to the error after the first call:

calls = {"count": 0}

def web_playback_for(ctx):
    calls["count"] += 1
    if calls["count"] == 1:
        return healthy_response(ctx)
    return WebPlaybackResponseSubscriptionError()

mock.endpoints.web_playback = web_playback_for

healthy_response(ctx) is your test's normal success path — the WebPlaybackResponseSuccess you would return when subscription is valid.

This pattern works for every keyed endpoint, not just web-playback.