Overarching project: https://github.com/airbnb/enzyme/projects/4

• Error Boundaries
  • componentDidCatch
    • Enzyme 3 couldn't test component when ComponentDidCatch happend #1255
  • Improve filenames in stack (Improve display of filenames in component stack facebook/react#12059)
  • getDerivedStateFromError (Support getDerivedStateFromError #2036)
• Portals
  • React adapter 16: portals and roots may render fragments #1710
  • Support of shallow for React16 Portals #1507
  • Support Portal components #252
• React.Fragment
  • Using <React.Fragment> prints warning with enzyme's mount with IE11 #1503
  • Adding Fragment support for shallow .find and .findWhere #1733
  • Enzyme matchers do not match correctly children of React Fragments #1799
• Rendering non-jsx
  • [Improved Fiber Support] Support Array-rendering components #1149
  • html() does not work on React components which return an array of elements #1178
  • React 16 fragments (rendering arrays and strings) unsupported #1213
  • Fix ShallowWrapper for array-rendering components #1498
• General issues around our use of private APIs
  • React toTree() handling mismatches #1512
• New context APIs in 16.3
  • New React context API adds new tag types #1509
  • Add support for react context element types, fixes #1509 #1513
  • dive() breaks when using the new context API. #1647
  • Invalid propType warning when rendering a Provider with no surrounding elements #1737
  • Dive shallow in a Context Consumer #1908
  • contextType (16.6) (wrappedComponent doesn't actually pass context values down in tests #2189, upstream PR)
  • better support for render props (Add renderProp to ShallowWrapper #1863)
• forwardRef
  • forwardRef: Enzyme Internal Error: unknown node with tag 14 #1604
  • Forward ref #1592
  • displayName set on forwardRef is not honored #1810 / [enzyme-adapter-react-{16,16.3}] [fix] forwardRef: respect .displayName #1817
• createRef
  • Using React 16 createRef #1704
• <React.StrictMode />: https://reactjs.org/docs/strict-mode.html
  • include mode in component stack (Include Modes in the component stack facebook/react#13240)
• <React.unstable_AsyncMode /> / <React.unstable_ConcurrentMode />:
• lazy/Suspense (16.6, Support Suspense #1917)
• memo (16.6, New memo feature from React 16.6 is not supported #1875)
• hooks (16.8, Testing Hooks with shallow: Invariant Violation #1938)
• Profiler (support unstable_Profiler #2054, fix: add Profiler support for adapter-react-16 #2233)