Swift test with CoreData in a Package

I'm glad I'm not the only one having this issue. It's like swift build doesn't even include the compiled .momd file (works just fine in Xcode!). I have tests that fail with

let modelPath = try XCTUnwrap(bundle.url(forResource: "TestModel", withExtension: "momd"), "Unable to find TestModel.momd")

and when I inspect the generated test bundles, I get the normal .xcdatamodeld. swift build appears to be missing a step that compiles Core Data models — something that xcodebuild knows how to do. It's likely this is intentionally decoupled from swift build and I have no idea how to fix it.

I think the problem you're having is because your package tests are in a different bundle. Packages define a separate test target in the Package.swift manifest.

To allow your tests to access resources, like the momd file, you'll need to declare a public symbol for them. This is similar to what you would need to do to access those resources from your app target.

For example, in a source file in your Swift package:

public static let momURL = Bundle.module.url(forResource: "MyModel", withExtension: "momd")

You can then use this to load the MOM in your unit tests:

let mom = NSManagedObjectModel(contentsOf: momURL!)