add failing test

test/cases/composes-async/async-1.css

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+:local .base {
+  composes: composed from './async-2.css';
+  background: blue;
+}

test/cases/composes-async/async-2.css

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+:local .composed {
+  background: green;
+}

test/cases/composes-async/expected/1.css

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+.base {
+  background: blue;
+}
+

test/cases/composes-async/expected/2.css

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+.composed {
+  background: green;
+}
+

test/cases/composes-async/index.js

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+import('./async-1.css');
+import('./async-2.css');

test/cases/composes-async/webpack.config.js

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+const Self = require('../../../');
+
+module.exports = {
+  entry: './index.js',
+  module: {
+    rules: [
+      {
+        test: /\.css$/,
+        use: [
+          Self.loader,
+          {
+            loader: 'css-loader',
+            options: {
+              localIdentName: '[local]'
+            }
+          }
+        ],
+      },
+    ],
+  },
+  plugins: [
+    new Self({
+      filename: '[name].css',
+    }),
+  ],
+};