feat: New strict option for React.Strict mode testing. (#415)

* Allow strict mode testing

* Add example of strict mode

Author: dmtrKovalenko

examples/react-scripts/src/App.cy-spec.js

@@ -8,7 +8,7 @@ import * as Child from './Child'
 
 describe('App', () => {
   it('renders learn react link', () => {
-    mount(<App />)
+    mount(<App />, { strict: true })
     cy.contains(/Learn React/)
   })
 

lib/index.d.ts

@@ -56,6 +56,11 @@ interface MountReactComponentOptions {
    * true by default.
    */
   log: boolean
+  /**
+   * Render component in React [strict mode](https://reactjs.org/docs/strict-mode.html)
+   * It activates additional checks and warnings for child components.
+   */
+  strict: boolean
 }
 
 type MountOptions = Partial<StyleOptions & MountReactComponentOptions>

lib/mount.ts

@@ -88,7 +88,11 @@ export const mount = (jsx: React.ReactElement, options: MountOptions = {}) => {
         key,
       }
 
-      const reactComponent = React.createElement(React.Fragment, props, jsx)
+      const reactComponent = React.createElement(
+        options.strict ? React.StrictMode : React.Fragment,
+        props,
+        jsx,
+      )
       // since we always surround the component with a fragment
       // let's get back the original component
       // @ts-ignore