feat: add toJSON to render; cleanup shallow (#35)

* feat: add toJSON to render; cleanup shallow

* Remove empty dependencies entry

* revert shallow import

* add docs

* add TS typings

src/__tests__/__snapshots__/render.test.js.snap

@@ -0,0 +1,3 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`toJSON 1`] = `"press me"`;

src/__tests__/render.test.js

@@ -161,3 +161,9 @@ test('unmount', () => {
   unmount();
   expect(fn).toHaveBeenCalled();
 });
+
+test('toJSON', () => {
+  const { toJSON } = render(<Button>press me</Button>);
+
+  expect(toJSON()).toMatchSnapshot();
+});

src/render.js

@@ -20,5 +20,6 @@ export default function render(
     ...queryByAPI(instance),
     update: renderer.update,
     unmount: renderer.unmount,
+    toJSON: renderer.toJSON,
   };
 }

src/shallow.js

@@ -1,6 +1,5 @@
 // @flow
 import * as React from 'react';
-import { isValidElementType } from 'react-is';
 import ShallowRenderer from 'react-test-renderer/shallow'; // eslint-disable-line import/no-extraneous-dependencies
 
 /**
@@ -10,15 +9,10 @@ export default function shallow(
   instance: ReactTestInstance | React.Element<*>
 ) {
   const renderer = new ShallowRenderer();
-  if (isValidElementType(instance)) {
-    // $FlowFixMe - instance is React.Element<*> in this branch
-    renderer.render(instance);
-  } else {
-    renderer.render(React.createElement(instance.type, instance.props));
-  }
-  const output = renderer.getRenderOutput();
+
+  renderer.render(React.createElement(instance.type, instance.props));
 
   return {
-    output,
+    output: renderer.getRenderOutput(),
   };
 }