Add basic tests (ref #81)

.eslintrc.json

@@ -2,7 +2,8 @@
     "env": {
         "browser": true,
         "node": true,
-        "es6": true
+        "es6": true,
+        "jest": true
     },
     "extends": "eslint:recommended",
     "parserOptions": {

jest/cssTransform.js

@@ -0,0 +1,14 @@
+'use strict';
+
+// This is a custom Jest transformer turning style imports into empty objects.
+// http://facebook.github.io/jest/docs/en/webpack.html
+
+module.exports = {
+  process() {
+    return 'module.exports = {};';
+  },
+  getCacheKey() {
+    // The output is always the same.
+    return 'cssTransform';
+  },
+};

package.json

@@ -64,6 +64,9 @@
     ],
     "moduleFileExtensions": [
       "js"
-    ]
+    ],
+    "moduleNameMapper": {
+      "\\.(css)$": "<rootDir>/jest/cssTransform.js"
+    }
   }
 }

src/simplebar.test.js

@@ -1 +1,25 @@
-import SimpleBar from './simplebar';
+import SimpleBar from './simplebar';
+
+beforeEach(() => {
+    jest.resetModules();
+
+    // Set up our document body
+    document.body.innerHTML = '<div id="simplebar"></div>';
+});
+
+test('should call constructor', () => {
+    const SimpleBar = require('./simplebar').default;
+    jest.mock('./simplebar');
+
+    const simpleBar = new SimpleBar(document.getElementById('simplebar'));
+
+    expect(SimpleBar).toHaveBeenCalledTimes(1);
+});
+test('should return right scroll element', () => {
+    const simpleBar = new SimpleBar(document.getElementById('simplebar'));
+    const scrollElementY = simpleBar.getScrollElement();
+    const scrollElementX = simpleBar.getScrollElement('x');
+
+    expect(scrollElementY).toBe(simpleBar.scrollContentEl);
+    expect(scrollElementX).toBe(simpleBar.contentEl);
+});