At this point, return to the Command Prompt and type the following command to test the web part in the local workbench:
gulp serve
The local workbench will load and insert the web part to the page.
At this point, we can test the web part to see if everything looks as expected. While testing web parts, it is good practice to insert multiple instances in the same page to see if they mess each other up.
You can also test the web part using SharePoint Workbench. The styles of SharePoint Workbench and a locally hosted Workbench look a little different. You might also see some minor changes when you try out the web part with different browsers.