Definitely Jest, I've tried few in the past and one of the great things of Jest is how easy it is to extend and customize if you are a library author with meani

Definitely Jest, I've tried few in the past and one of the great things of Jest is how easy it is to extend and customize if you are a library author with meaningful messages. So I wrote a small test runner for React (`react-test`) and added few custom Jest matchers, so you can do: const button = $(<Button>Hello World</Button>); expect(button).toHaveClass('btn'); expect(button).toHaveText('Hello World');