An instance of the Completable class doesn't emit a value at all. It can be used to notify the user of task completion. In addition, it can be used when we delete an item from a database, for instance.

The following example code shows a case of deleting an item from a database:

Completable.fromAction { Database.delete() }
        .test()
        .assertComplete()

The test method returns an instance of the TestObservable class.