C# – Convert string to C# code

cnunitnunit-2.5

in the current NUnit version, I can parameterized TestFixture and instantiated it multiple times. E.g.:

[TestFixture("var1")]  
[TestFixture("var2")]  
[TestFixture("var3")]  
public class MyTestFixture  
{  
    private string var;  

    public MyTestFixture(string var)  
    {  
        this.var = var;  
    }  

    ...  

}

This will instantiate the MyTestFixture 3 times with the argument parameter. My problem is the current NUnit doesn't have datasource feature for TextFixture attribute (only TestCaseSource). I need to instantiate the TestFixture based on the data input, and each TestFixture has a different sets of test case data input. No problem with the Test case data driven, thanks to the TestCaseSource. But how can I do this for the TestFixture attribute?

My idea is to generate the TestFixture attribute on the fly then change it to code string and insert into the test code, e.g.: something like this:

ConvertToCode(GenerateTestFixture());  
public class MyTestFixture  
{  
   ...  
}

How can I do this? Or are there a better way?

Thank you very much for your help.

Best regards,
Edward

Best Answer

Creating attributes for your method on the fly is possible but hard. You're better off finding another approach.

Attributes (e.g. [TestFixture]) of the kind you have are read by the compiler when your code is compiled and inserted in to your code automatically.

To generate your own attributes for classes you'll need to use something like Reflection.Emit to modify generated assemblies as a post-build step for the project. This is like writing assembly language directly (you'd be creating MSIL) which might be fun but is not easy and would make your code very hard to maintain!

An alternative approach might be to have an enum control the test cases, and have a method that checks the enum and returns the appropriate data:

public enum TestController
{
    Value1,
    Value2,
    Value3
}

[TestFixture(TestController.Value1)]   
[TestFixture(TestController.Value2)]   
[TestFixture(TestController.Value3)]   
public class MyTestFixture   
{   
    public MyTestFixture(TestController testController)   
    {   
        var dataForTest = GetDataForTest(testController);
    }   

    ...   

}

The method GetDataForTest() would then have some kind of switch statement to generate the data.

An alternative approach might be to use a type rather than an enum, then instantiate the type in the GetDataForTest() method and call a factory method - but I think that might be a bit overcomplicated.

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – Convert a string to an enum in C#

In .NET Core and .NET Framework ≥4.0 there is a generic parse method:

Enum.TryParse("Active", out StatusEnum myStatus);

This also includes C#7's new inline out variables, so this does the try-parse, conversion to the explicit enum type and initialises+populates the myStatus variable.

If you have access to C#7 and the latest .NET this is the best way.

Original Answer

In .NET it's rather ugly (until 4 or above):

StatusEnum MyStatus = (StatusEnum) Enum.Parse(typeof(StatusEnum), "Active", true);

I tend to simplify this with:

public static T ParseEnum<T>(string value)
{
    return (T) Enum.Parse(typeof(T), value, true);
}

Then I can do:

StatusEnum MyStatus = EnumUtil.ParseEnum<StatusEnum>("Active");

One option suggested in the comments is to add an extension, which is simple enough:

public static T ToEnum<T>(this string value)
{
    return (T) Enum.Parse(typeof(T), value, true);
}

StatusEnum MyStatus = "Active".ToEnum<StatusEnum>();

Finally, you may want to have a default enum to use if the string cannot be parsed:

public static T ToEnum<T>(this string value, T defaultValue) 
{
    if (string.IsNullOrEmpty(value))
    {
        return defaultValue;
    }

    T result;
    return Enum.TryParse<T>(value, true, out result) ? result : defaultValue;
}

Which makes this the call:

StatusEnum MyStatus = "Active".ToEnum(StatusEnum.None);

However, I would be careful adding an extension method like this to string as (without namespace control) it will appear on all instances of string whether they hold an enum or not (so 1234.ToString().ToEnum(StatusEnum.None) would be valid but nonsensical) . It's often be best to avoid cluttering Microsoft's core classes with extra methods that only apply in very specific contexts unless your entire development team has a very good understanding of what those extensions do.

Best Answer

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – Convert a string to an enum in C#

Original Answer

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