How To Set Elements Of An Array Of A Private Type Using Visual Studio Shadows

Visual Studio uses Publicize to create accessors public for private members and types of a type.


But when you try to set elements of a private array of elements of a private type, things get complicated.


Imagine this hypothetic class to test:

public static class MyClass
{
private static readonly MyInnerClass[] myArray = new MyInnerClass[10];

public static bool IsEmpty()
{
foreach (var item in myArray)
{
if ((item != null) && (!string.IsNullOrEmpty(item.Field)))
{
return false;
}
}

return true;
}

private class MyInnerClass
{
public string Field;
}
}


If I want to write a test for the case when the array has “non empty” entries, I need to setup the array first.


Using the accessors generated by Visual Studio, I would write something like this:

[TestClass()]
public class MyClassTest
{
[TestMethod()]
public void IsEmpty_NotEmpty_ReturnsFalse()
{
for (int i = 0; i < 10; i++)
{
MyClass_Accessor.myArray[i] = new MyClass_Accessor.MyInnerClass { Field = i.ToString() };
}

bool expected = false;
bool actual;

actual = MyClass.IsEmpty();

Assert.AreEqual(expected, actual);
}
}


But the test will fail because, although the elements of the private array myArray can be read as MyClass_Accessor.MyInnerClass instances, they can’t be written as such.


To do so, the test would have to be written like this:

[TestClass()]
public class MyClassTest
{
[TestMethod()]
public void IsEmpty_NotEmpty_ReturnsFalse()
{
for (int i = 0; i < 10; i++)
{
MyClass_Accessor.ShadowedType.SetStaticArrayElement("myArray", new MyClass_Accessor.MyInnerClass { Field = i.ToString() }.Target, i);
}

bool expected = false;
bool actual;

actual = MyClass.IsEmpty();

Assert.AreEqual(expected, actual);
}
}


But, this way, we loose all the strong typing of the accessors because we need to write the name of the array field.


Because the accessor for the field is a property, we could write a set of extension methods that take care of getting the field name for us. Something like this:

public static class PrivateypeExtensions
{
public static void SetStaticArrayElement<T>(this PrivateType self, Expression<Func<T[]>> expression, T value, params int[] indices)
{
object elementValue = (value is BaseShadow) ? (value as BaseShadow).Target : value;

self.SetStaticArrayElement(
((PropertyInfo)((MemberExpression)(expression.Body)).Member).Name,
elementValue,
indices);
}

public static void SetStaticArrayElement<T>(this PrivateType self, Expression<Func<T[]>> expression, BindingFlags invokeAttr, T value, params int[] indices)
{
object elementValue = (value is BaseShadow) ? (value as BaseShadow).Target : value;

self.SetStaticArrayElement(
((PropertyInfo)((MemberExpression)(expression.Body)).Member).Name,
invokeAttr,
elementValue,
indices);
}
}


Now, we can write the test like this:

[TestClass()]
public class MyClassTest
{
[TestMethod()]
public void IsEmpty_NotEmpty_ReturnsFalse()
{
for (int i = 0; i < 10; i++)
{
MyClass_Accessor.ShadowedType.SetStaticArrayElement(() => MyClass_Accessor.myArray, new MyClass_Accessor.MyInnerClass { Field = i.ToString() }, i);
}

bool expected = false;
bool actual;

actual = MyClass.IsEmpty();

Assert.AreEqual(expected, actual);
}
}


It’s not the same as the first form, but it’s strongly typed and we’ll get a compiler error instead of a test run error if we change the name of the myArray field.


You can find this and other tools on the PauloMorgado.TestTools on CodePlex.

Comments are closed.