How do you unit test a widget’s timeline logic when the provider’s Context cannot be created in a test?

The provider’s methods receive a TimelineProviderContext (family, preview flag, size), and that type has no public initializer: the check shows the compiler refusing TimelineProviderContext() (“cannot be constructed because it has no accessible initializers”). So you cannot call getTimeline(in:completion:) from a test with a fabricated context, and you should not try to subclass or mock it. The design answer is to keep the provider a thin adapter: it reads the family and the data, then calls a pure function such as makeTimeline(now:data:family:) in a shared module, which returns a Timeline (a plain value you can inspect: entries, policy).

Test that function with injected now and data, including the failure and empty cases from the previous question, and snapshot-test the view for each entry with a fixed rendering mode. Then use Xcode’s widget previews and a device for what tests cannot see: the real budget, rendering modes and process limits. Link only the shared module into the test target, not the extension, so tests do not depend on extension entry points.