refactor: use shallow to fix react warning (#1236)

Switcher test (`src\tests\unit\tests\DetailsView\components\switcher.test.tsx`) is showing warnings (while running the unit tests): **componentWillRecieveProps has been renamed...**

The warning mention to update `DropdownBase` which is on the office fabric side (one more reason to update our office ui fabric version) but we can fix this warning by not `mount`ing the tested component. Instead, we can use `shallow` which will not call to the base component.

Author: smoralesd

src/tests/unit/tests/DetailsView/components/switcher.test.tsx

@@ -1,6 +1,6 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
-import { mount, shallow } from 'enzyme';
+import { shallow } from 'enzyme';
 import { Dropdown, IDropdownOption } from 'office-ui-fabric-react/lib/Dropdown';
 import * as React from 'react';
 import { IMock, Mock, Times } from 'typemoq';
@@ -40,7 +40,7 @@ describe('Switcher', () => {
         actionCreatorMock
             .setup(creator => creator.sendPivotItemClicked(DetailsViewPivotType[DetailsViewPivotType.assessment]))
             .verifiable(Times.once());
-        const wrapper = mount<Switcher>(<Switcher {...defaultProps} />);
+        const wrapper = shallow<Switcher>(<Switcher {...defaultProps} />);
         const dropdown = wrapper.find(Dropdown);
 
         expect(wrapper.state().selectedKey).toBe(DetailsViewPivotType.fastPass);