public async void KeyDoesNotExist()
        {
            using (var context = DatabaseHelper.CreateContext())
            {
                var    repo = new PassphraseRepository(context);
                string key  = await repo.GetOrAdd();

                Assert.True(Guid.TryParse(key, out Guid result));
            }
        }
        public async void KeyExist()
        {
            using (var context = DatabaseHelper.CreateContext())
            {
                Passphrase passphrase = new Passphrase {
                    Key = Guid.NewGuid().ToString()
                };
                context.Passphrase.Add(passphrase);
                context.SaveChanges();

                var    repo = new PassphraseRepository(context);
                string key  = await repo.GetOrAdd();

                Assert.Equal(passphrase.Key, key);
            }
        }