Stub test double: a predefined collaborator

A test stub is a collaborator that has canned returns so that we can control the indirect input of the SUT.

Considering the example of the fake, we create a Stub that already has two tasks:

class StubTaskStoreWithTwoTasks: TaskStore {
    private(set) var allTasks = [Task(), Task()]

    func add(task: Task) {
        allTasks.append(task)
    }
}

The test is as follows:

func testAddATaskToPreloadedTasks() {
    let taskManager = TaskManager(store: StubTaskStoreWithTwoTasks())
    taskManager.add(task: Task())
    XCTAssertEqual(taskManager.count, 3)
}