Dependencies in @Tests are not reset but are in XCTest

[ph1ps]

Hello,
I've recently been rewriting some dependency related tests in swift-testing but I came across a discrepancy to XCTest, where I could not find anything in the documentation. Consider this dependency:

struct TestDependency: TestDependencyKey, Sendable {
  let add: @Sendable (Int) -> Void
  
  static var testValue: TestDependency {
    let array = OSAllocatedUnfairLock<Int?>(initialState: nil)
    return .init { newValue in
      array.withLock { value in
        if value != nil {
          fatalError()
        } else {
          value = newValue
        }
      }
    }
  }
}

extension DependencyValues {
  var test: TestDependency {
    get { self[TestDependency.self] }
    set { self[TestDependency.self] = newValue }
  }
}

And then following XCTestCase:

import XCTest

class TestCase: XCTestCase {
  @Dependency(\.test) var test
  func testSomething() {
    test.add(1)
  }
}

The fatalError() will never trigger here, because after each test function, the cached dependency is reset (I think). However, the same code with swift-testing:

import Testing

@Suite(.serialized) struct TestSuite {
  @Dependency(\.test) var test
  @Test func testSomething() {
    test.add(1)
  }
}

... does run into the fatalError. Is this just to be expected, because of differences in swift-testing and XCTest? If yes, I think if it was not yet documented it makes sense to document this somewhere. Or are there workarounds to get the same behavior?

Edit 1: You will need to Run "TestSuite" repeatedly, to run into this problem
Edit 2: Same happens with SwiftTestingTests cachePollution1 and cachePollution2

[mbrandonw]

Edit 1: You will need to Run "TestSuite" repeatedly, to run into this problem

I believe we have documentation on this somewhere, but currently .dependency does not work with parameterized tests or repeatedly run tests. We are currently doing some hacky things to support .dependency in the first place, but really we need new tools from Swift Testing to support this properly. Those tools are coming, hopefully in Swift 6.1, called Test Scoping Traits.

[mbrandonw]

It's worth mentioning that if you use withDependencies and surround the body of your view instead of using .dependency things will work correctly, even in parameterized and repeated tests.

[ph1ps]

Right, I think I‘ve seen the docs on parameterized tests, maybe I‘ve missed the part with repeatedly run tests.

Thank you for clarifying.

[Infinity-James]

Thanks.