1<===> same/input.scss
2a {b: selector-unify(".c", ".c")}
3
4<===> same/output.css
5a {
6  b: .c;
7}
8
9<===>
10================================================================================
11<===> different/input.scss
12a {b: selector-unify(".c", ".d")}
13
14<===> different/output.css
15a {
16  b: .c.d;
17}
18