Minimal Example of Unit Testing Core Data

DatabaseManagerTests.swift

import XCTest
import CoreData
@testable import DoIt

/// Test the DatabaseManager against a Mock Database Manager.
///
/// Note that testing is done against a mock version of the database, linking
/// to the memory instead of the actual SQLite file.
///
/// - Author:
///     Rafael Papallas
class DatabaseManagerTests: XCTestCase {
    
    override func setUp() {
        super.setUp()
    }
    
    /// This will test if the database was able to insert a new task instance.
    ///
    /// Note that this will not test if the instance could be located after
    /// insertion, is just going to check if the `.saveOrUpdate(instance:)`
    /// returned true, which will indicate that the insertion was successful.
    func testSuccessfulTaskInsertion_WithAllAttributesSet() {
        // Create new task instance.
        let mockDatabaseManager = MockDatabaseManager()

        let newTask = mockDatabaseManager.getEmptyTaskInstance
        newTask.title = "Test #1"
                
        XCTAssertTrue(mockDatabaseManager.saveOrUpdate(instance: newTask))
    }
}