PrivateObject Unit Tester
AndrewSeven was kind enough to direct me to a blog by James Newkirk briefly introducing the PrivateObject class available at part of the VS Team System framework.
I was intrigued enough to start investigating and ended up implementing what I think is a close interpretation of this class, shown below.
The primary interface is the constructor which accepts an assembly qualified type name as the first parameter (used by Type.GetType()). The second parameter is optional and is passed as the arguments to instantiate the type; these arguments determine the constructor signature to choose.
As documented in the Type.GetType() method, the qualifiedTypeName should be of the form MyNamespace.MyClass,MyAssemblyBaseName.
Here's the code:
using System;
using System.Reflection;
using System.Security.Permissions;
#region .
/// <summary>
/// This utility class uses reflection to wrap an instance of a/// class to gain access to non-public members of that class.
/// This is an internal utility class used for unit testing.
/// </summary>
#endregion
public class PrivateObject
{
private const BindingFlags bindingFlags= BindingFlags.Instance | BindingFlags.NonPublic;
private Type type; // type of class to manage
private object instance; // managed instance of type
private ReflectionPermission perm; // for non-public members
#region .
/// <summary>
/// Initializes a new instance wrapping a new instance of the/// target type. One PrivateObject manages exactly one instance
/// of a target type.
/// </summary>
/// <param name="qualifiedTypeName">The qualified name of the type./// This should include the full assembly qualified name including
/// the namespace, for example "MyNamespace.MyType,MyAssemblyBaseName"
/// where MyNamespace is the dotted-notation namespace, MyType is the
/// name of the type and MyAssemblyBaseName is the base name of the
/// assembly containing the type.
/// </param>
/// <param name="args">An optional array of parameters to pass to/// the constructor. If this argument is not specified then the
/// default constructor is used. Otherwise, a constructor that
/// matches the number and type of parameters is used.
/// </param>
#endregion
public PrivateObject (string qualifiedTypeName, params object[] args)
{
perm = new ReflectionPermission(PermissionState.Unrestricted);
perm.Demand();type = Type.GetType(qualifiedTypeName);
Type[] types = new Type[args.Length];
for (int i=0; i < args.Length; i++)
{
types[i] = args[i].GetType();
}instance = type.GetConstructor(bindingFlags,null,types,null).Invoke(args);
}
#region .
/// <summary>
/// Gets the instance of the managed object.
/// </summary>
#endregion
public object Instance
{
get { return instance; }
}
#region .
/// <summary>
/// Gets the value of a non-public field (member variable) of the/// managed type.
/// </summary>
/// <param name="name">The name of the non-public field to/// interrogate</param>
/// <returns>A value whose type is specific to the field.</returns>
#endregion
public object GetField (string name)
{
return type.GetField(name,bindingFlags).GetValue(instance);
}
#region .
/// <summary>
/// Gets the value of a non-public property of the managed type.
/// </summary>
/// <param name="name">The name of the non-public property to/// interrogate.</param>
/// <returns>A value whose type is specific to the property.</returns>
#endregion
public object GetProperty (string name)
{
return type.GetProperty(name,bindingFlags).GetValue(instance,null);
}
#region .
/// <summary>
/// Invokes the non-public method of the managed type.
/// </summary>
/// <param name="name">The name of the non-public method to invoke.</param>
/// <param name="args">And optional array of typed parameters to pass to the
/// method. If this argument is not specified then the routine searches
/// for a method with a signature that contains not parameters. Otherwise,
/// the procedure searches for a method with the number and type of parameters
/// specified.
/// </param>
/// <returns>A value who type is specific to the invoked method.</returns>
#endregion
public object Invoke (string name, params object[] args)
{
Type[] types = new Type[args.Length];
for (int i=0; i < args.Length; i++)
{
types[i] = args[i].GetType();
}return type.GetMethod(name,bindingFlags,null,types,null).Invoke(instance,args);
}
#region .
/// <summary>
/// Sets the value of a non-public field (member variable) of the managed type.
/// </summary>
/// <param name="name">The name of the non-public field to modify.</param>
/// <param name="val">A value whose type is specific to the field.</param>
#endregion
public void SetField (string name, object val)
{
type.GetField(name,bindingFlags).SetValue(instance,val);
}
#region .
/// <summary>
/// Sets the value of a non-public property of the managed type.
/// </summary>
/// <param name="name">The name of the non-public property to modify.</param>
/// <param name="val">A value whose type is specific to the property.</param>
#endregion
public void SetProperty (string name, object val)
{
type.GetProperty(name,bindingFlags).SetValue(instance,val,null);
}
}
