unit testing - c# - Assert Expressions -

i have 'example' class , create unit test it. take on classes below:

public class example  {     private readonly calculator _calculator;      public example(icalculator calculator)     {         _calculator = calculator;     }      public void calculate()     {         _calculator.execute(operation => operation.subtract());     } }  public interface ioperation {      void sum();     void subtract(); }  public inferface icalculator {      void execute(action<ioperation> action); }  public class calculator {     public void execute(action<ioperation> action){} } 

what want create unit test class verify method example class calculate calls _calculator.execute passing parameter operation.subtract(). possible?

i know how mock icalculator , verify execute being called once, have no idea how validade if execute method called using operation.subtract() parameter instead of operation.sum().

i using nunit create unit tests. here can see how unit test class @ moment:

[testfixture] public class exampletests  {     [test]     public void test1()     {         var calculator = new mock<icalculator>();         var subject = new example(calculator.object);          subject.calculate();          calculator.verify(x => x.execute(it.isany<action<ioperation>>()), times.once);     } } 

hope can understand english, sorry that.

you cannot directly verify lambda passed can go around actually invoking said lambda yet mock:

var calculator = new mock<icalculator>(); var operation = new mock<ioperation>(); // when calculator's execute called, invoke it's argument (action<ioperation>) // mocked ioperation later verified calculator     .setup(c => c.execute(it.isany<action<ioperation>>()))     .callback<action<ioperation>>(args => args(operation.object)); var example = new example(calculator.object);  example.calculate();  calculator.verify(c => c.execute(it.isany<action<ioperation>>())); operation.verify(o => o.subtract());