c# - NUnit test for Void function (Sending Email) -

i have void function, sends email. need write tests ​​function. how can done?

public void sendadminmail(string subject, string body, string adminaddress)     {          var email = email.             from(configurationmanager.appsettings["mail.noreply.address"].tostring(cultureinfo.invariantculture)).             to(adminaddress).             subject(subject).             body(body).             usingclient(getofficeclient());         email.message.subjectencoding = encoding.utf8;         email.message.bodyencoding = encoding.utf8;          email.send();     } 

in context hard - unless you'll able switch email somehow through reflection (as interestingly pointed out juhan_h in answer, maybe not hard nowadays ;) ).

typical solution provide interface class, example interface emailfactory. you'd have:

private emailfactory emailfactory; public void sendadminmail(string subject, string body, string adminaddress) {     var email = emailfactory         .from(configurationmanager                   .appsettings["mail.noreply.address"]                   .tostring(cultureinfo.invariantculture))         .to(adminaddress)         .subject(subject)         .body(body)         .usingclient(getofficeclient());      email.message.subjectencoding = encoding.utf8;     email.message.bodyencoding = encoding.utf8;      email.send(); } 

and provide stub of factory class, create email mocks on verify correct behavior.