test: fix invalid test and source map test (#481)

test/cases/no-source-map/expected/main.css

@@ -0,0 +1,4 @@
+body {
+  background: red;
+}
+

test/cases/no-source-map/index.js

@@ -0,0 +1 @@
+import './style.css';

test/cases/no-source-map/style.css

@@ -0,0 +1,3 @@
+body {
+  background: red;
+}

test/cases/no-source-map/webpack.config.js

@@ -0,0 +1,30 @@
+import Self from '../../../src';
+
+module.exports = {
+  entry: './index.js',
+  // Required to disable source maps in webpack@4
+  devtool: false,
+  module: {
+    rules: [
+      {
+        test: /\.css$/,
+        use: [
+          {
+            loader: Self.loader,
+          },
+          {
+            loader: 'css-loader',
+            options: {
+              sourceMap: false,
+            },
+          },
+        ],
+      },
+    ],
+  },
+  plugins: [
+    new Self({
+      filename: '[name].css',
+    }),
+  ],
+};

test/cases/source-map/webpack.config.js

@@ -10,9 +10,6 @@ module.exports = {
         use: [
           {
             loader: Self.loader,
-            options: {
-              sourceMap: true,
-            },
           },
           {
             loader: 'css-loader',