public void ReturnsKeysAsync()
{
// Arrange
const string key1 = "TestKey1";
const string key2 = "TestKey2";
_sut.Clear();
var item1 = new TestObject(1, "Jane Smith");
var item2 = new TestObject(2, "John Smith");
_sut.SetItem(key1, item1);
_sut.SetItem(key2, item2);
// Act
var keyNames = _sut.KeysAsync().Result.ToList();
// Assert
Assert.Collection(keyNames,
item => Assert.Equal(key1, item),
item => Assert.Equal(key2, item));
}