Add some unit tests via jest for the start

Fixes: #14

package.json

@@ -7,10 +7,11 @@
     "build": "tsc",
     "watch": "tsc -w",
     "lint": "tslint --fix -p tsconfig.json -c tslint.json",
-    "tests": " ",
+    "tests": "jest",
+    "tests:watch": "jest --watch",
     "test": "yarn tests && yarn lint",
     "precommit": "lint-staged",
-    "prepare": "yarn clean && yarn build"
+    "prepublishOnly": "yarn clean && yarn build"
   },
   "repository": {
     "type": "git",
@@ -35,16 +36,19 @@
   "devDependencies": {
     "@types/inquirer": "^0.0.35",
     "@types/ip": "^0.0.30",
+    "@types/jest": "^23.3.4",
     "@types/lodash": "^4.14.71",
     "@types/mkdirp": "^0.5.0",
     "@types/node": "^7.0.18",
     "@types/webpack": "^3.0.10",
     "@types/webpack-sources": "^0.1.2",
     "@types/yargs": "^8.0.2",
     "husky": "^0.14.3",
+    "jest": "^23.6.0",
     "lint-staged": "^4.1.3",
     "prettier": "^1.6.1",
     "rimraf": "^2.6.2",
+    "ts-jest": "^23.10.4",
     "tslint": "^5.2.0",
     "tslint-config-prettier": "^1.5.0",
     "tslint-plugin-prettier": "^1.3.0",
@@ -86,5 +90,16 @@
     "printWidth": 120,
     "singleQuote": true,
     "parser": "babylon"
+  },
+  "jest": {
+    "transform": {
+      ".ts": "ts-jest"
+    },
+    "testRegex": "(/__tests__/.*\\.(test|spec))\\.(ts|js)$",
+    "moduleFileExtensions": [
+      "ts",
+      "js",
+      "json"
+    ]
   }
 }

src/plugins/shared/__tests__/JSRuleFinder.test.ts

@@ -0,0 +1,26 @@
+import { Builder } from '../../../Builder';
+import JSRuleFinder from '../JSRuleFinder';
+
+describe('JSRuleFinder', () => {
+  it('should create js rule if it does not exist', () => {
+    // tslint:disable-next-line
+    const builder: Builder = {} as Builder;
+    builder.config = {
+      module: { rules: [] }
+    };
+    const rule = new JSRuleFinder(builder).findAndCreateJSRule();
+    expect(rule).toHaveProperty('test');
+  });
+
+  it('should find js rule if it exists', () => {
+    // tslint:disable-next-line
+    const builder: Builder = {} as Builder;
+    const regex = /\.js$/;
+    builder.config = {
+      module: { rules: [{ test: /abc/ }, { test: regex }, { test: /def/ }] }
+    };
+    const rule = new JSRuleFinder(builder).findAndCreateJSRule();
+    expect(rule).toHaveProperty('test');
+    expect(rule.test).toEqual(regex);
+  });
+});