Swift test with CoreData in a Package

Question

Created May ’21

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I'm getting an error running unit tests with swift test that succeed when I run them from Xcode. The units and my CoreData model are in a Swift Package. I'm loading the model using Bundle.module like so:

Code Block 		Bundle.module.url(forResource: PersistenceController.modelName, withExtension: "momd")

The unit tests are able to load the CoreData model when run from Xcode and also using the xcodebuild test command line.

When I run the tests with swift test I get the following error:

Code Block error: cannot find type 'MyEntity' in scope

Is there something more to be done to enable running CoreData unit tests from a Package using swift tests?

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Answer 1

kreeger OP

Jul ’21

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.

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Answer 2

kharrison OP

Jul ’21

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!)

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