     public typealias Container = MockContainer
 
     public let containers: [Container]
-    public let containersByIdentifier: [Container.Identifier: Container]
+    public let containersByIdentifier: [PackageReference: Container]
 
     public init(containers: [MockContainer]) {
         self.containers = containers

        self.init(name: name, dependencies: dependencies)
    }

    private init(
        name: Identifier,
        dependencies: [String: [Dependency]] = [:]
        ) {
        self.name = name

    }

    func testResolutionAvoidingConflictResolutionDuringDecisionMaking() {
        builder.serve(root: "root", with: ["a": v1Range, "b": v1Range])
        builder.serve("a", at: v1)
        builder.serve("a", at: v1_1, with: ["b": v2Range])
        builder.serve("b", at: v1)
        builder.serve("b", at: v1_1)
        builder.serve("b", at: v2)

        let resolver = builder.create()
        let result = resolver.solve(root: rootRef, pins: [])

        switch result {
