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