Implement testing library (#2)

Co-authored-by: Eric NGUYEN <enguyen@techform.fr>
Reviewed-on: https://git.siklos-chaneru.duckdns.org/Siklos/svg-layout-designer-react/pulls/2

.eslintrc.cjs

@@ -21,6 +21,7 @@ module.exports = {
   ],
   rules: {
     'space-before-function-paren': ['error', 'never'],
+    indent: ['warn', 2],
     semi: ['warn', 'always']
   }
 };