Normalize selector function input/output format specs (#1521)

Also add a missing named parameter spec for selector-extend()

spec/core_functions/selector/append.hrx

@@ -78,19 +78,45 @@ a {
 
 <===>
 ================================================================================
-<===> input/input.scss
-// The full set of possible input formats is tested with `selector-parse()`;
-// this spec just verifies one example for `selector-append()`.
-a {b: selector-append((c, d e), (f, g h))}
+<===> format/README.md
+These specs verify that all the arguments to `selector-append()` can take the
+parsed selector format, and that the function returns a selector in that format.
+The full set of possible input formats is tested with `selector-parse()`; this
+spec just verifies one example for each parameter.
 
-<===> input/output.css
+<===>
+================================================================================
+<===> format/input/initial/input.scss
+a {b: selector-append((c, d e), f)}
+
+<===> format/input/initial/output.css
+a {
+  b: cf, d ef;
+}
+
+<===>
+================================================================================
+<===> format/input/later/input.scss
+a {b: selector-append(c, (d, e f))}
+
+<===> format/input/later/output.css
+a {
+  b: cd, ce f;
+}
+
+<===>
+================================================================================
+<===> format/output/input.scss
+$result: selector-append("c d, e f", "g");
 a {
-  b: cf, cg h, d ef, d eg h;
+  result: $result;
+  structure: $result == ("c" "dg", "e" "fg");
 }
 
-<===> input/output-libsass.css
+<===> format/output/output.css
 a {
-  b: cf, d ef, cg h, d eg h;
+  result: c dg, e fg;
+  structure: true;
 }
 
 <===>

spec/core_functions/selector/extend/format.hrx

@@ -0,0 +1,95 @@
+<===> input/non_string/README.md
+These specs verify that all the arguments to `selector-extend()` can take the
+parsed selector format, and that the function returns a selector in that format.
+The full set of possible input formats is tested with `selector-parse()`; this
+spec just verifies one example for each parameter.
+
+<===>
+================================================================================
+<===> input/non_string/selector/input.scss
+a {b: selector-extend((c, d c), "c", "e")}
+
+<===> input/non_string/selector/output.css
+a {
+  b: c, e, d c;
+}
+
+<===>
+================================================================================
+<===> input/non_string/extendee/options.yml
+---
+:todo:
+- sass/libsass#3068
+
+<===> input/non_string/extendee/input.scss
+a {b: selector-extend("c.d", (c, ".d"), ".e")}
+
+<===> input/non_string/extendee/output.css
+a {
+  b: c.d, .e;
+}
+
+<===>
+================================================================================
+<===> input/non_string/extender/input.scss
+a {b: selector-extend("c", "c", (d, e f))}
+
+<===> input/non_string/extender/output.css
+a {
+  b: c, d, e f;
+}
+
+<===>
+================================================================================
+<===> input/multiple_extendees/compound/input.scss
+a {b: selector-extend("c.d", "c.d", ".e")}
+
+<===> input/multiple_extendees/compound/output.css
+a {
+  b: c.d, .e;
+}
+
+<===>
+================================================================================
+<===> input/multiple_extendees/list/options.yml
+---
+:todo:
+- sass/libsass#3067
+
+<===> input/multiple_extendees/list/input.scss
+a {b: selector-extend("c.d", "c, .d", ".e")}
+
+<===> input/multiple_extendees/list/output.css
+a {
+  b: c.d, .e;
+}
+
+<===>
+================================================================================
+<===> input/multiple_extendees/list_of_compound/options.yml
+---
+:todo:
+- sass/libsass#3067
+
+<===> input/multiple_extendees/list_of_compound/input.scss
+a {b: selector-extend("c.d.e.f", "c.d, .e.f", ".g")}
+
+<===> input/multiple_extendees/list_of_compound/output.css
+a {
+  b: c.d.e.f, .g;
+}
+
+<===>
+================================================================================
+<===> output/input.scss
+$result: selector-extend("c d, e f", "g", "g");
+a {
+  result: $result;
+  structure: $result == ("c" "d", "e" "f");
+}
+
+<===> output/output.css
+a {
+  result: c d, e f;
+  structure: true;
+}

spec/core_functions/selector/extend/named.hrx

@@ -0,0 +1,7 @@
+<===> input.scss
+a {b: selector-extend($selector: "c.d", $extendee: "c", $extender: "e")}
+
+<===> output.css
+a {
+  b: c.d, e.d;
+}