linq mutators for Union, Intersect, Concat & Except

[jnyrup]

I was wondering how to mutate code that involved the following LINQ methods

• Union()
• Intersect()
• Concat()
• Except()

One idea was this mapping

Original	Mutated
Union()	Intersect()
Intersect()	Union()
Concat()	Except()
Except()	Concat()

Alternatively would it be within the scope of Stryker or possible at all, to mutate the IEnumerable<T> parameter with Enumerable.Empty<T>()?

[richardwerkman]

I Like these additions to the linq mutator. I'm not sure what your plan is with the Enumerable.Empty<T>(). Should it replace the whole linq query?

If you'd like to help us more with our mutators you could check out this issue: stryker-mutator/stryker-handbook#33

[jnyrup]

@richardwerkman
My idea with Enumerable.Empty<T>() was to introduce two mutants of e.g. a.Concat(b):

• Enumerable.Empty<T>().Concat(b)
• a.Concat(Enumerable.Empty<T>())

I had a look at the other issue, but I don't really have any opinions on mutant levels, except that it sounds useful.

[richardwerkman]

That could prove hard as these methods are not always directly called on the list itself. They are often called like:

a.ToList().Concat(b);

which would become:

a.Enumerable.Empty<T>().Concat(b)

That would not compile of couse. I think swapping the methods with their "opposite" method does the job as well and is a much easier mutation. So I'd rather go for your first suggestion.

And thanks for taking a look at the other issue, good to know it sounds useful.