Added a test.

Author: kelp404

__tests__/lib/__snapshots__/shared-state.js.snap

@@ -1,5 +1,26 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`Call the setter of useState() to update the different part. 1`] = `true`;
+
+exports[`Call the setter of useState() to update the different part. 2`] = `undefined`;
+
+exports[`Call the setter of useState() to update the different part. 3`] = `
+Object {
+  "child": false,
+}
+`;
+
+exports[`Call the setter of useState() to update the different part. 4`] = `
+Object {
+  "test": Object {
+    "child": true,
+  },
+  "testX": Object {
+    "child": false,
+  },
+}
+`;
+
 exports[`Call useState() to get the state and the setter. 1`] = `
 Object {
   "test": true,

__tests__/lib/shared-state.js

@@ -122,3 +122,27 @@ test('Call useState() twice to make sure it did not assign setter again.', () =>
   renderer.create(React.createElement(component, null));
   expect(shareState.useState).toBeCalled();
 });
+
+test('Call the setter of useState() to update the different part.', () => {
+  const shareState = new SharedState();
+  jest.spyOn(shareState, 'useState');
+  const childComponent = () => {
+    const [state] = shareState.useState('test.child', true);
+    expect(state).toMatchSnapshot();
+    return React.createElement('div', null);
+  };
+
+  const parentComponent = () => {
+    const [state, setState] = shareState.useState('testX');
+    expect(state).toMatchSnapshot();
+    if (!state) {
+      setState({child: false});
+    }
+
+    return React.createElement('div', null);
+  };
+
+  renderer.create(React.createElement(childComponent, null));
+  renderer.create(React.createElement(parentComponent, null));
+  expect(shareState.state).toMatchSnapshot();
+});