[New] mount: add renderProp

docs/api/ReactWrapper/renderProp.md

@@ -0,0 +1,85 @@
+# `.renderProp(propName, ...args) => ReactWrapper`
+
+Calls the current wrapper's property with name `propName` and the `args` provided.
+Returns the result in a new wrapper.
+
+NOTE: can only be called on wrapper of a single non-DOM component element node.
+
+#### Arguments
+
+1.  `propName` (`String`):
+1.  `...args` (`Array<Any>`):
+
+This essentially calls `wrapper.prop(propName)(...args)`.
+
+#### Returns
+
+`ReactWrapper`: A new wrapper that wraps the node returned from the render prop.
+
+#### Examples
+
+##### Test Setup
+
+```jsx
+class Mouse extends React.Component {
+  constructor() {
+    super();
+    this.state = { x: 0, y: 0 };
+  }
+
+  render() {
+    const { render } = this.props;
+    return (
+      <div
+        style={{ height: '100%' }}
+        onMouseMove={(event) => {
+          this.setState({
+            x: event.clientX,
+            y: event.clientY,
+          });
+        }}
+      >
+        {render(this.state)}
+      </div>
+    );
+  }
+}
+
+Mouse.propTypes = {
+  render: PropTypes.func.isRequired,
+};
+```
+
+```jsx
+const App = () => (
+  <div style={{ height: '100%' }}>
+    <Mouse
+      render={(x = 0, y = 0) => (
+        <h1>
+          The mouse position is ({x}, {y})
+        </h1>
+      )}
+    />
+  </div>
+);
+```
+
+##### Testing with no arguments
+
+```jsx
+const wrapper = mount(<App />)
+  .find(Mouse)
+  .renderProp('render');
+
+expect(wrapper.equals(<h1>The mouse position is 0, 0</h1>)).to.equal(true);
+```
+
+##### Testing with multiple arguments
+
+```jsx
+const wrapper = mount(<App />)
+  .find(Mouse)
+  .renderProp('render', [10, 20]);
+
+expect(wrapper.equals(<h1>The mouse position is 10, 20</h1>)).to.equal(true);
+```

docs/api/mount.md

@@ -120,6 +120,9 @@ Get a wrapper with the first ancestor of the current node to match the provided
 #### [`.render() => CheerioWrapper`](ReactWrapper/render.md)
 Returns a CheerioWrapper of the current node's subtree.
 
+#### [`.renderProp(key) => ReactWrapper`](ReactWrapper/renderProp.md)
+Returns a wrapper of the node rendered by the provided render prop.
+
 #### [`.text() => String`](ReactWrapper/text.md)
 Returns a string representation of the text nodes in the current render tree.
 

packages/enzyme-test-suite/test/ReactWrapper-spec.jsx

@@ -4959,6 +4959,68 @@ describeWithDOM('mount', () => {
     });
   });
 
+  describe('.renderProp()', () => {
+    it('returns a wrapper around the node returned from the render prop', () => {
+      class Foo extends React.Component {
+        render() {
+          return <div className="in-foo" />;
+        }
+      }
+      class Bar extends React.Component {
+        render() {
+          const { render: r } = this.props;
+          return <div className="in-bar">{r()}</div>;
+        }
+      }
+
+      const wrapperA = mount(<div><Bar render={() => <div><Foo /></div>} /></div>);
+      const renderPropWrapperA = wrapperA.find(Bar).renderProp('render');
+      expect(renderPropWrapperA.find(Foo)).to.have.lengthOf(1);
+
+      const wrapperB = mount(<div><Bar render={() => <Foo />} /></div>);
+      const renderPropWrapperB = wrapperB.find(Bar).renderProp('render');
+      expect(renderPropWrapperB.find(Foo)).to.have.lengthOf(1);
+
+      const stub = sinon.stub().returns(<div />);
+      const wrapperC = mount(<div><Bar render={stub} /></div>);
+      stub.resetHistory();
+      wrapperC.find(Bar).renderProp('render', 'one', 'two');
+      expect(stub.args).to.deep.equal([['one', 'two']]);
+    });
+
+    it('throws on host elements', () => {
+      class Div extends React.Component {
+        render() {
+          const { children } = this.props;
+          return <div>{children}</div>;
+        }
+      }
+
+      const wrapper = mount(<Div />).childAt(0);
+      expect(wrapper.is('div')).to.equal(true);
+      expect(() => wrapper.renderProp('foo')).to.throw();
+    });
+
+    wrap()
+      .withOverride(() => getAdapter(), 'wrap', () => undefined)
+      .it('throws with a react adapter that lacks a `.wrap`', () => {
+        class Foo extends React.Component {
+          render() {
+            return <div className="in-foo" />;
+          }
+        }
+        class Bar extends React.Component {
+          render() {
+            const { render: r } = this.props;
+            return <div className="in-bar">{r()}</div>;
+          }
+        }
+
+        const wrapper = mount(<div><Bar render={() => <div><Foo /></div>} /></div>);
+        expect(() => wrapper.find(Bar).renderProp('render')).to.throw(RangeError);
+      });
+  });
+
   describe('lifecycle methods', () => {
     describeIf(is('>= 16.3'), 'getDerivedStateFromProps', () => {
       let spy;

packages/enzyme/src/ReactWrapper.js

@@ -1,5 +1,6 @@
 import cheerio from 'cheerio';
 import flat from 'array.prototype.flat';
+import has from 'has';
 
 import {
   containsChildrenSubArray,
@@ -779,6 +780,40 @@ class ReactWrapper {
     return this.props()[propName];
   }
 
+  /**
+   * Returns a wrapper of the node rendered by the provided render prop.
+   *
+   * @param {String} propName
+   * @returns {ReactWrapper}
+   */
+  renderProp(propName, ...args) {
+    const adapter = getAdapter(this[OPTIONS]);
+    if (typeof adapter.wrap !== 'function') {
+      throw new RangeError('your adapter does not support `wrap`. Try upgrading it!');
+    }
+
+    return this.single('renderProp', (n) => {
+      if (n.nodeType === 'host') {
+        throw new TypeError('ReactWrapper::renderProp() can only be called on custom components');
+      }
+      if (typeof propName !== 'string') {
+        throw new TypeError('`propName` must be a string');
+      }
+      const props = this.props();
+      if (!has(props, propName)) {
+        throw new Error(`no prop called “${propName}“ found`);
+      }
+      const propValue = props[propName];
+      if (typeof propValue !== 'function') {
+        throw new TypeError(`expected prop “${propName}“ to contain a function, but it holds “${typeof prop}“`);
+      }
+
+      const element = propValue(...args);
+      const wrapped = adapter.wrap(element);
+      return this.wrap(wrapped, null, this[OPTIONS]);
+    });
+  }
+
   /**
    * Returns the key assigned to the current node.
    *