Shared DI Container causes test race conditions

[HunterKF]

I am currently working on adding Unit Testing to my code and am running into race conditions. I followed the docs on how to set up the test with the container, but still the tests seem to share the same container.

Here is an example of my unit test. Test 1 always succeeds. Tests 2 and 3 are the ones that seem to share the same container. One of them consistently fails, and it switches between the two. Is there some step I missed or is this a bug?

@Suite(.container)
struct GenericViewModelTests {
    
    @Test("Updates items correctly") // Test 1
    func testUpdatesItems() {
        
        // Given
        let id = "123"
        let mock = MockDataRepo(mockItems: [Item(), Item()])
        Container.shared.dataHelper.register { mock }
        
        let viewModel = GenericViewModel()
        
        // When
        viewModel.fetchData(for: id)
        
        // Then
        #expect(mock.fetchCalled == true)
        #expect(viewModel.items.count == 1)
    }
    
    @Test("Handles empty result") // Test 2
    func testHandlesEmptyResult() {
        
        // Given
        let id = "123"
        let mock = MockDataRepo(mockItems: [])
        Container.shared.dataHelper.register { mock }
        
        let viewModel = GenericViewModel()
        
        // When
        viewModel.fetchData(for: id)
        
        // Then
        #expect(mock.fetchCalled == true)
        #expect(viewModel.items.isEmpty)
    }
    
    @Test("Sets error on nil result") // Test 3
    func testSetsErrorOnNilResult() {
        
        // Given
        let id = "error"
        let mock = MockDataRepo(fetchOverride: { _, completion in
            completion(nil)
        })
        Container.shared.dataHelper.register { mock }
        
        let viewModel = GenericViewModel()
        
        // When
        viewModel.fetchData(for: id)
        
        // Then
        #expect(mock.fetchCalled == true)
        #expect(viewModel.hasErrors == true)
        #expect(viewModel.items.isEmpty)
    }
}

For context, here is the MockRepo

class MockDataRepo: DataRepoProtocol {
    var fetchCalled = false
    var mockItems: [Item]
    let id: UUID
    let label: String
    var fetchOverride: ((String, @escaping ([Item]?) -> Void) -> Void)?

    init(
        mockItems: [Item] = [],
        label: String = "mock",
        fetchOverride: ((String, @escaping ([Item]?) -> Void) -> Void)? = nil
    ) {
        self.mockItems = mockItems
        self.id = UUID()
        self.label = label
        self.fetchOverride = fetchOverride
    }

    func fetchItems(for id: String, onCompletion: @escaping ([Item]?) -> Void) {
        fetchCalled = true
        if let override = fetchOverride {
            override(id, onCompletion)
        } else {
            onCompletion(mockItems)
        }
    }
}

[hmlongco]

No clue. Please provide the missing Factory definition and enough code (mock or otherwise) to be able to run the tests as shown.

[hmlongco]

So, I added the following to a project...

import FactoryKit
import SwiftUI

extension Container {
    var dataHelper: Factory<DataRepoProtocol> {
        self { fatalError() }
    }
}

protocol DataRepoProtocol: Sendable {
    func fetchItems(for id: String, onCompletion: @escaping ([DataRepoItem]?) -> Void)
}

class MockDataRepo: @unchecked Sendable, DataRepoProtocol {
    var fetchCalled = false
    var mockItems: [DataRepoItem]
    let id: UUID
    let label: String
    var fetchOverride: ((String, @escaping ([DataRepoItem]?) -> Void) -> Void)?

    init(
        mockItems: [DataRepoItem] = [],
        label: String = "mock",
        fetchOverride: ((String, @escaping ([DataRepoItem]?) -> Void) -> Void)? = nil
    ) {
        self.mockItems = mockItems
        self.id = UUID()
        self.label = label
        self.fetchOverride = fetchOverride
    }

    func fetchItems(for id: String, onCompletion: @escaping ([DataRepoItem]?) -> Void) {
        fetchCalled = true
        if let override = fetchOverride {
            override(id, onCompletion)
        } else {
            onCompletion(mockItems)
        }
    }
}

struct DataRepoItem {
    let id: UUID = UUID()
}

class GenericViewModel {
    var items: [DataRepoItem] = []
    var hasErrors: Bool?
    @Injected(\.dataHelper) var dataHelper: DataRepoProtocol
    func fetchData(for id: String) {
        dataHelper.fetchItems(for: id) { items in
            if let items = items {
                self.items = items
                self.hasErrors = false
            } else {
                self.hasErrors = true
            }
        }
    }
}

And then added the following tests.

#if swift(>=6.1)

@testable import RequestBuilderDemo

import FactoryKit
import FactoryTesting
import SwiftUI
import Testing

@Suite(.container)
struct GenericViewModelTests {
    
    @Test("Updates items correctly") // Test 1
    func testUpdatesItems() {
        
        // Given
        let id = "123"
        let mock = MockDataRepo(mockItems: [DataRepoItem(), DataRepoItem()])
        Container.shared.dataHelper.register { mock }
        
        let viewModel = GenericViewModel()
        
        // When
        viewModel.fetchData(for: id)
        
        // Then
        #expect(mock.fetchCalled == true)
        #expect(viewModel.items.count == 2)
    }
    
    @Test("Handles empty result") // Test 2
    func testHandlesEmptyResult() {
        
        // Given
        let id = "123"
        let mock = MockDataRepo(mockItems: [])
        Container.shared.dataHelper.register { mock }
        
        let viewModel = GenericViewModel()
        
        // When
        viewModel.fetchData(for: id)
        
        // Then
        #expect(mock.fetchCalled == true)
        #expect(viewModel.items.isEmpty)
    }
    
    @Test("Sets error on nil result") // Test 3
    func testSetsErrorOnNilResult() {
        
        // Given
        let id = "error"
        let mock = MockDataRepo(fetchOverride: { _, completion in
            completion(nil)
        })
        Container.shared.dataHelper.register { mock }
        
        let viewModel = GenericViewModel()
        
        // When
        viewModel.fetchData(for: id)
        
        // Then
        #expect(mock.fetchCalled == true)
        #expect(viewModel.hasErrors == true)
        #expect(viewModel.items.isEmpty)
    }
}

#endif

And told Xcode to run the tests repeatedly, 1000 times.

No problems.

One question, however, are you adding the FactoryKit library to the test target? AKA:

If so, DON'T DO THAT! 😀

Importing FactoryKit directly into the test target masks the version in the main project, and will cause issues.

If not, then I'm back to no clue, since as far as I can see, the container trait is working as expected. If you can create a MVP that demonstrates the issue, send it do me.

[HunterKF]

Thank you for your time. I should have specified more about it and which Factory version I was using. Turns out it didn't work in 2.5.1, but when updating to 2.5.3, it works. Now on to more testing, thanks again!