Add test for getCssModule

Author: Barak Igal

test/api.test.js

@@ -0,0 +1,10 @@
+import MiniCssExtractPlugin from '../src';
+
+import { getCompiler } from './helpers'
+
+describe('API', () => {
+  it('should return the same CssModule when same webpack instance provided', () => {
+    const { webpack } = getCompiler('');
+    expect(MiniCssExtractPlugin.getCssModule(webpack)).toEqual(MiniCssExtractPlugin.getCssModule(webpack));
+  });
+});