add better test for comma-separated selector support

Signed-off-by: Yoshua Wuyts <[email protected]>

Closes #1

Author: ahdinosaur

test/fixture-out.css

@@ -15,6 +15,8 @@
 #hello-world h2#thing {}
 #hello-world #thing h3 {}
 
+#hello-world .a, #hello-world .b, #hello-world .c {}
+
 @media screen and (max-width: 42rem) {
   #hello-world #another .thing > x-here {}
 }

test/fixture.css

@@ -15,6 +15,8 @@ h1.title {}
 h2#thing {}
 #thing h3 {}
 
+.a, .b, .c {}
+
 @media screen and (max-width: 42rem) {
   #another .thing > x-here {}
 }