Problem Description:

Consider I have piece of code var a = Substitute.For<ISomeIterface>();. After some time I do no longer use this variable a in code, so my IDE shows warning with quick fix to delete declaration of this variable, I accept this quick fix, but instead of removing whole statement he removes only left part of assigment. After quick fix, this line looks like this: Substitute.For<ISomeIterface>();. I had such cases many time and its very inconvenient, because after IDE code cleanup you have to look for such leftover Substitute.For<T>(); calls.

Cause:

This behavior is caused because IDE does not know that Substitute.For<ISomeIterface>(); in fact is Pure method, meaning that it just returns value and does not have any side effects.

Fix:

This has a very easy fix: Add PureAttribute (See Docs) to Substitute.For<T>() (and all other overloads).