HM-48. Внедрена система тестирования jest (#17)

package.json

@@ -4,12 +4,13 @@
   "description": "",
   "main": "index.js",
   "scripts": {
-    "build": "webpack --mode=production",
+    "build": "npm run test && webpack --mode=production",
     "start": "webpack-dev-server --open",
     "dev": "webpack-dev-server",
     "docs": "rm -rf out && documentation build src/** -f html -o out",
     "show:docs": "lite-server --baseDir=\"out\"",
-    "lint": "eslint -c .eslintrc.json src --fix"
+    "lint": "eslint -c .eslintrc.json src --fix",
+    "test": "jest"
   },
   "repository": {
     "type": "git",
@@ -37,10 +38,12 @@
     "eslint": "^7.4.0",
     "eslint-loader": "^4.0.2",
     "eslint-plugin-import": "^2.22.0",
+    "eslint-plugin-jest": "^23.18.0",
     "file-loader": "^6.0.0",
     "html-loader": "^1.1.0",
     "html-webpack-plugin": "^4.3.0",
     "image-webpack-loader": "^6.0.0",
+    "jest": "^26.1.0",
     "mini-css-extract-plugin": "^0.9.0",
     "postcss-import": "^12.0.1",
     "postcss-loader": "^3.0.0",