[Color 4] Add tests for lab() (#1928)

spec/core_functions/color/hsl/error/one_arg.hrx

@@ -159,7 +159,7 @@ Error: $channels: Expected lightness "var(--foo) / 0.4" to be a number.
 a {b: hsl(append((), 0 100% 100%, $separator: slash))}
 
 <===> slash_list/too_few_elements/error
-Error: Only 2 slash-separated elements allowed, but 1 was passed.
+Error: $channels: Only 2 slash-separated elements allowed, but 1 was passed.
   ,
 1 | a {b: hsl(append((), 0 100% 100%, $separator: slash))}
   |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -173,7 +173,7 @@ Error: Only 2 slash-separated elements allowed, but 1 was passed.
 a {b: hsl(list.slash(0 100% 100%, 0.4, 1))}
 
 <===> slash_list/too_many_elements/error
-Error: Only 2 slash-separated elements allowed, but 3 were passed.
+Error: $channels: Only 2 slash-separated elements allowed, but 3 were passed.
   ,
 2 | a {b: hsl(list.slash(0 100% 100%, 0.4, 1))}
   |       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

spec/core_functions/color/lab/_utils.scss

@@ -0,0 +1,27 @@
+@use 'sass:color';
+@use 'sass:list';
+@use 'sass:meta';
+
+@function -real-channel($color, $channel) {
+  @if color.is-missing($color, $channel) {
+    @return none;
+  } @else {
+    @return color.channel($color, $channel);
+  }
+}
+
+@mixin inspect($color) {
+  a {
+    value: $color;
+    @if meta.type-of($color) == string {
+      type: string;
+    } @else {
+      channels: list.slash(
+        -real-channel($color, 'lightness')
+          -real-channel($color, 'a')
+          -real-channel($color, 'b'),
+        -real-channel($color, 'alpha')
+      );
+    }
+  }
+}

spec/core_functions/color/lab/alpha.hrx

@@ -0,0 +1,145 @@
+<===> transparent/input.scss
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(0 255 127 / 0));
+
+<===> transparent/output.css
+a {
+  value: lab(0% 255 127 / 0);
+  channels: 0% 255 127 / 0;
+}
+
+<===>
+================================================================================
+<===> opaque/input.scss
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(1% 2 3 / 1));
+
+<===> opaque/output.css
+a {
+  value: lab(1% 2 3);
+  channels: 1% 2 3 / 1;
+}
+
+<===>
+================================================================================
+<===> partial/input.scss
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(1% 2 3 / 0.4));
+
+<===> partial/output.css
+a {
+  value: lab(1% 2 3 / 0.4);
+  channels: 1% 2 3 / 0.4;
+}
+
+<===>
+================================================================================
+<===> percent/input.scss
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(1% 2 3 / 40%));
+
+<===> percent/output.css
+a {
+  value: lab(1% 2 3 / 0.4);
+  channels: 1% 2 3 / 0.4;
+}
+
+<===>
+================================================================================
+<===> named/input.scss
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab($channels: 1% 2 3 / 0.4));
+
+<===> named/output.css
+a {
+  value: lab(1% 2 3 / 0.4);
+  channels: 1% 2 3 / 0.4;
+}
+
+<===>
+================================================================================
+<===> slash_list/input.scss
+@use "sass:list";
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(list.slash(1% 2 3, 0.4)));
+
+<===> slash_list/output.css
+a {
+  value: lab(1% 2 3 / 0.4);
+  channels: 1% 2 3 / 0.4;
+}
+
+<===>
+================================================================================
+<===> none/slash/b/input.scss
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(1% 2 none / 0.4));
+
+<===> none/slash/b/output.css
+a {
+  value: lab(1% 2 none / 0.4);
+  channels: 1% 2 none / 0.4;
+}
+
+<===>
+================================================================================
+<===> none/slash/alpha/input.scss
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(1% 2 3 / none));
+
+<===> none/slash/alpha/output.css
+a {
+  value: lab(1% 2 3 / none);
+  channels: 1% 2 3 / none;
+}
+
+<===>
+================================================================================
+<===> none/slash/b_and_alpha/input.scss
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(1% 2 none / none));
+
+<===> none/slash/b_and_alpha/output.css
+a {
+  value: lab(1% 2 none / none);
+  channels: 1% 2 none / none;
+}
+
+<===>
+================================================================================
+<===> none/slash_list/b/input.scss
+@use 'sass:list';
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(list.slash(1% 2 none, 0.4)));
+
+<===> none/slash_list/b/output.css
+a {
+  value: lab(1% 2 none / 0.4);
+  channels: 1% 2 none / 0.4;
+}
+
+<===>
+================================================================================
+<===> none/slash_list/alpha/input.scss
+@use 'sass:list';
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(list.slash(1% 2 3, none)));
+
+<===> none/slash_list/alpha/output.css
+a {
+  value: lab(1% 2 3 / none);
+  channels: 1% 2 3 / none;
+}
+
+<===>
+================================================================================
+<===> none/slash_list/b_and_alpha/input.scss
+@use 'sass:list';
+@use 'core_functions/color/lab/utils';
+@include utils.inspect(lab(list.slash(1% 2 none, none)));
+
+<===> none/slash_list/b_and_alpha/output.css
+a {
+  value: lab(1% 2 none / none);
+  channels: 1% 2 none / none;
+}