Add test to reproduce warnings

Author: emmenko

test/fixtures/similar-matches/input.css

@@ -0,0 +1,20 @@
+@custom-selector :--foo .foo;
+@custom-selector :--foo-bar .foo .bar;
+@custom-selector :--foo-baz .foo .baz;
+@custom-selector :--foo-bar-baz .foo .bar .baz;
+
+:--foo {
+    color: red;
+}
+
+:--foo-bar {
+    color: green;
+}
+
+:--foo-baz {
+    color: black;
+}
+
+:--foo-bar-baz {
+    color: blue;
+}

test/fixtures/similar-matches/output.css

@@ -0,0 +1,15 @@
+.foo {
+    color: red;
+}
+
+.foo .bar {
+    color: green;
+}
+
+.foo .baz {
+    color: black;
+}
+
+.foo .bar .baz {
+    color: blue;
+}

test/index.js

@@ -30,6 +30,7 @@ test("@custom-selector", function(t) {
   compareFixtures(t, "multiline", "should transform multiline")
   compareFixtures(t, "some-hyphen", "should transform some hyphen")
   compareFixtures(t, "matches", "should transform matches selector")
+  compareFixtures(t, "similar-matches", "should transform matches selector")
 
   compareFixtures(t, "extension", "should transform local extensions", {
     extensions: {