Test private static method throws MissingMethodException

Question

I have this class:

public class MyClass
{
   private static int GetMonthsDateDiff(DateTime d1, DateTime d2)
   {
     // implementatio
   }
}

Now I am implementing unit test for it. Since the method is private, I have following code:

MyClass myClass = new MyClass();
PrivateObject testObj = new PrivateObject(myClass);
DateTime fromDate = new DateTime(2015, 1, 1);
DateTime toDate = new DateTime(2015, 3, 17);
object[] args = new object[2] { fromDate, toDate };
int res = (int)testObj.Invoke("GetMonthsDateDiff", args); //<- exception

An exception of type 'System.MissingMethodException' occurred in mscorlib.dll but was not handled in user code Additional information: Attempted to access a missing member.

What Am I doing wrong? The method exists..

score 27 · Accepted Answer · answered Feb 16 '15 at 18:08

27

It is a static method, so use PrivateType instead of PrivatObject to access it.

See PrivateType.

answered Feb 16 '15 at 18:08

Brian Rasmussen

114,645
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10

And `InvokeStatic()` instead of `Invoke()` to call it. – Nigel Touch Feb 24 '16 at 15:36

score 11 · Answer 2 · answered Mar 31 '16 at 11:25

Use below code with PrivateType

MyClass myClass = new MyClass();
PrivateType testObj = new PrivateType(myClass.GetType());
DateTime fromDate = new DateTime(2015, 1, 1);
DateTime toDate = new DateTime(2015, 3, 17);
object[] args = new object[2] { fromDate, toDate };
(int)testObj.InvokeStatic("GetMonthsDateDiff", args)

rae1 · Answer 3 · 2015-02-16T18:13:35.920

The Invoke method is the one that cannot be found. The Object class does not have an Invoke method. I think you might be trying to use this Invoke, which is part of System.Reflection.

You can use it like this,

var myClass = new MyClass();
var fromDate = new DateTime(2015, 1, 1);
var toDate = new DateTime(2015, 3, 17);
var args = new object[2] { fromDate, toDate };

var type = myClass.GetType();
// Because the method is `static` you use BindingFlags.Static 
// otherwise, you would use BindingFlags.Instance 
var getMonthsDateDiffMethod = type.GetMethod(
    "GetMonthsDateDiff",
    BindingFlags.Static | BindingFlags.NonPublic);
var res = (int)getMonthsDateDiffMethod.Invoke(myClass, args);

However, you should not be trying to test a private method; it is much too specific and subject to change. You should instead make it public of a DateCalculator class which is private in MyClass, or perhaps, making it internal, so you can only use inside your assembly.

EZI · Answer 4 · 2015-02-16T18:19:34.757

1

int res = (int)typeof(MyClass).InvokeMember(
                name: "GetMonthsDateDiff", 
                invokeAttr: BindingFlags.NonPublic |
                            BindingFlags.Static |
                            BindingFlags.InvokeMethod,
                binder: null, 
                target: null, 
                args: args);

edited Feb 16 '15 at 18:19

answered Feb 16 '15 at 18:02

EZI

15,209
2
27
33

score 1 · Answer 5 · answered Sep 12 '16 at 11:45

MyClass myClass = new MyClass();
PrivateObject testObj = new PrivateObject(myClass);
DateTime fromDate = new DateTime(2015, 1, 1);
DateTime toDate = new DateTime(2015, 3, 17);
object[] args = new object[2] { fromDate, toDate };

//The extra flags
 BindingFlags flags = BindingFlags.Static| BindingFlags.NonPublic
int res = (int)testObj.Invoke("GetMonthsDateDiff",flags, args);

Test private static method throws MissingMethodException

5 Answers5