to contain

  • <ReactTestRenderer> [not] to contain [with all children] [with all wrappers] [with all classes] [with all attributes] <ReactElement|string>
  • <ReactTestRenderer> [not] to contain [exactly] <ReactElement|string>

It's possible to check for a part of the subtree, without testing the entire returned tree. This allows you to test specific elements, without writing brittle tests that break when the structure changes.

Assuming the following component output

const MyComponent = () => (
  <div>
    <span className="top">one</span>
    <span className="middle">two</span>
    <span className="bottom">three</span>
  </div>
)
 
var renderer = TestRenderer.create(<MyComponent/>);
// This will pass, as `<span className="middle">two</span>` can be found in the renderers output
expect(renderer, 'to contain', <span>two</span>);

Notice that the extra className="middle" in the <span className="middle">two</span> is ignored, in a similar way to the to have rendered assertion.

You can override this behaviour by using 'to contain exactly', and 'to contain with all children'

// This will fail, as `<span>two</span>` cannot be found in the renderers output, due to
// the missing `className="middle"` prop
expect(renderer, 'to contain exactly', <span>two</span>);
expected
<div>
  
<span className="top">
one
</span>
<span className="middle">
two
</span>
<span className="bottom">
three
</span>
</div>
to contain exactly <span>
two
</span>
 
the best match was
<span className="middle" 
//
 
className should be removed
>
  
two
</span>

The same thing applies to children for 'to contain' as for 'to have rendered'.