public void Single_should_throw_when_aggregate_is_null( [Values(false, true)] bool async) { IAggregateFluent <Person> subject = null; Action action; if (async) { action = () => subject.SingleAsync().GetAwaiter().GetResult(); } else { action = () => subject.Single(); } action.ShouldThrow <ArgumentNullException>().And.ParamName.Should().Be("aggregate"); }