c# - Modifying a private static readonly field -

i have large application reads parameters configuration file.

i'm writing unit tests class generates result after performing operations both parameter , value read configuration file:

internal static class password {     private static readonly byte password_private_key         = configfile.readbyte("password_private_key");      public static byte generate(byte passwordpublickey); } 

in unit test, know values password.generate() method should return given password_private_keyand password_public_key. i'd password_private_key value used defined in unit test class, not in configuration file:

[testmethod] public void passwordgenerate_calculatedproperly() {     byte passwordpublickey = 0x22;     password_accessor.password_private_key = 0xf0;     byte expectedgenerated = 0xaa;      byte generated = password_accessor.generate(passwordpublickey);      assert.areequal(expectedgenerated, generated); } 

is there way can write private static readonly thru code, don't have rely configuration file tests?

to in clean way, need make password more testable. this, consider design:

internal static class password {     public static void configure(iprivatekeyprovider keyprovider)     {         keyprovider = keyprovider;     }      public static byte generate(byte passwordpublickey); // use keyprovider      private static iprivatekeyprovider* keyprovider; }  internal interface iprivatekeyprovider {     byte getprivatekey(); }  internal class configprivatekeyprovider : iprivatekeyprovider {     private static readonly byte password_private_key          = configfile.readbyte("password_private_key");      public byte getprivatekey()     {         return password_private_key;     } }  internal class privatekeyproviderstub : iprivatekeyprovider {     public privatekeyproviderstub(byte privatekey)     {         this.privatekey = privatekey;     }      public byte getprivatekey()     {         return this.privatekey;     } } 

now production code can use configprivatekeyprovider , tests can use privatekeyproviderstub.

it bit simplified retain password static class. i'd recommend refactoring ordinary class, singleton maybe if it's appropriate.

note there many testing frameworks allow generate mocks , stubs conveniently on fly (rhino mocks example), there no need manually implement privatekeyproviderstub.