c# - Extension method doesn't throw exception as expected -

i have following extension methods:

public static t toobject<t>(this datarow row) t : new() {     if (row == null) throw new argumentnullexception("row");      // }  public static ienumerable<t> toobject<t>(this datatable table) t : new() {     if (table == null) throw new argumentnullexception("table");      // } 

and respective tests:

[testmethod] [expectedexception(typeof(argumentnullexception))] public void nulldatarow() {     // arrange     datarow row = null;      // act     row.toobject<somedata>(); }  [testmethod] [expectedexception(typeof(argumentnullexception))] public void nulldatatable() {     // arrange     datatable table = null;      // act     table.toobject<somedata>(); } 

the datarow test passes (it throws argumentnullexception normally) while datatable one doesn't (doesn't hit method nor throw anything).

i have absolutely no idea why datatable test isn't working (and datarow 1 normal!).

(at first thought bug in visual studio, the ci service use accused same)

i'll assume ienumerable<t> isn't fun, , extension method iterator.

such iterator, doesn't execute point of throwing exception until start iterating it.