C# Unit testing class with a private constructor

cnetnunitunit testing

Ok so i just got an assignment where i have to perform unit testing on a class with a private constructor.

Now how am i suppose to do unit testing without initializing a class when all the methods are also non static.

Is there any way i can do unit testing(without reflection)on a class with a private constructor ?

Best Answer

If you cannot make the class public, you can still test it easily by creating an instance of it this way:

var anInstance = (YourPrivateClass)Activator.CreateInstance(typeof(YourPrivateClass), true);

This will give you an instance of your class that you can then populate.

Another helpful testing bit is if you have internal methods (not private), you can access them by making internals visible to your test class. You add this line in assemblyinfo.cs of the class with the internal methods:

[assembly: InternalsVisibleTo("YourSolution.Tests")]

Related Solutions

C# – Calling the base constructor in C#

Modify your constructor to the following so that it calls the base class constructor properly:

public class MyExceptionClass : Exception
{
    public MyExceptionClass(string message, string extrainfo) : base(message)
    {
        //other stuff here
    }
}

Note that a constructor is not something that you can call anytime within a method. That's the reason you're getting errors in your call in the constructor body.

Java – How to test a class that has private methods, fields or inner classes

Update:

Some 10 years later perhaps the best way to test a private method, or any inaccessible member, is via @Jailbreak from the Manifold framework.
@Jailbreak Foo foo = new Foo();
// Direct, *type-safe* access to *all* foo's members
foo.privateMethod(x, y, z);
foo.privateField = value;
This way your code remains type-safe and readable. No design compromises, no overexposing methods and fields for the sake of tests.

If you have somewhat of a legacy Java application, and you're not allowed to change the visibility of your methods, the best way to test private methods is to use reflection.

Internally we're using helpers to get/set private and private static variables as well as invoke private and private static methods. The following patterns will let you do pretty much anything related to the private methods and fields. Of course, you can't change private static final variables through reflection.

Method method = TargetClass.getDeclaredMethod(methodName, argClasses);
method.setAccessible(true);
return method.invoke(targetObject, argObjects);

And for fields:

Field field = TargetClass.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, value);

Notes:
1. TargetClass.getDeclaredMethod(methodName, argClasses) lets you look into private methods. The same thing applies for getDeclaredField.
2. The setAccessible(true) is required to play around with privates.

Best Answer

Related Solutions

C# – Calling the base constructor in C#

Java – How to test a class that has private methods, fields or inner classes

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