Fix CoreData test warnings (#1276)

BitwardenShared/Core/Platform/Services/Stores/DataStore.swift

@@ -19,6 +19,17 @@ enum StoreType {
 /// A data store that manages persisting data across app launches in Core Data.
 ///
 class DataStore {
+    // MARK: Type Properties
+
+    /// The managed object model representing the entities in the database schema. CoreData throws
+    /// warnings if this is instantiated multiple times (e.g. in tests), which is fixed by making
+    /// it static.
+    private static let managedObjectModel: NSManagedObjectModel = {
+        let modelURL = Bundle(for: DataStore.self).url(forResource: "Bitwarden", withExtension: "momd")!
+        let managedObjectModel = NSManagedObjectModel(contentsOf: modelURL)!
+        return managedObjectModel
+    }()
+
     // MARK: Properties
 
     /// A managed object context which executes on a background queue.
@@ -45,9 +56,7 @@ class DataStore {
     init(errorReporter: ErrorReporter, storeType: StoreType = .persisted) {
         self.errorReporter = errorReporter
 
-        let modelURL = Bundle(for: type(of: self)).url(forResource: "Bitwarden", withExtension: "momd")!
-        let managedObjectModel = NSManagedObjectModel(contentsOf: modelURL)!
-        persistentContainer = NSPersistentContainer(name: "Bitwarden", managedObjectModel: managedObjectModel)
+        persistentContainer = NSPersistentContainer(name: "Bitwarden", managedObjectModel: Self.managedObjectModel)
         let storeDescription: NSPersistentStoreDescription
         switch storeType {
         case .memory: