add some unit tests and a gitlab ci

.gitlab-ci.yml

@@ -0,0 +1,20 @@
+image: node:latest
+
+stages:
+  - test
+  - build
+
+cache:
+  paths:
+    - node_modules/
+
+test:
+  stage: test
+  script:
+    - npm install
+    - npm run test
+
+build:
+  stage: build
+  script:
+    - npm run build

src/elements/Tag.js

@@ -13,7 +13,7 @@ class Tag extends React.Component {
     render() {
         // todo onclick events correctlyy
         return (
-            <button className='tagbtn' onClick={this.props.onClick}>{this.props.children}</button>
+            <button className='tagbtn' onClick={this.props.onClick} data-testid="Test-Tag">{this.props.children}</button>
         );
     }
 }

src/elements/Tag.test.js

@@ -0,0 +1,16 @@
+import React from "react";
+import ReactDom from 'react-dom'
+import Tag from './Tag'
+import {render} from '@testing-library/react'
+import "@testing-library/jest-dom"
+
+it('renders without crashing ', function () {
+    const div = document.createElement("div");
+    ReactDom.render(<Tag/>,div);
+    ReactDom.unmountComponentAtNode(div);
+});
+
+it('renders childs correctly', function () {
+    const {getByTestId} = render(<Tag>test</Tag>);
+    expect(getByTestId("Test-Tag")).toHaveTextContent("test");
+});