test(postcss-merge-rules): test container queries

Related to #1489, but the code snippet
in that issue is not valid CSS

packages/postcss-merge-rules/test/index.js

@@ -150,6 +150,22 @@ test(
   passthroughCSS('@media print{h1{display:block}}h1{color:red}')
 );
 
+test(
+  'should not merge across container queries',
+  passthroughCSS(
+    `@container (min-width: 200px) {
+  .mobile {
+     display: none;
+  }
+}
+@container (max-width: 100px) {
+  .notMobile {
+     display: none;
+  }
+}`
+  )
+);
+
 test(
   'should perform partial merging of selectors',
   processCSS(
@@ -843,4 +859,5 @@ test(
     'h1{color:#001;color:#002;color:#003}h2{color:#001;color:#002}'
   )
 );
+
 test.run();