Enzyme to React Testing Library Migration

Goal

Migrate enzyme tests to @testing-library/react as a 1:1 port — preserve existing test intent without refactoring toward integration-style testing or removing mocks.

Core principles

• Preserve test intent. Do not rewrite test logic or remove mocks. Add mocks where enzyme's shallow rendering previously hid missing providers/contexts.
• Cut dead tests. Enzyme tests component trees, not DOM. Tests that assert on elements never actually rendered in the DOM should be removed with a comment explaining why.
• No new data-test-subj for snapshots. Use container.children[0] for root-element snapshots instead of adding a test locator just for snapshotting.

Migration workflow

1. Replace enzyme imports with RTL imports.
2. Replace shallow() / mount() with render().
3. Migrate selectors and assertions.
4. Update or delete snapshots (--updateSnapshot).
5. Run the test and fix any missing mocks/providers that enzyme's shallow rendering was hiding.

Import changes

Before

import { shallow, mount } from 'enzyme';
import { shallowWithIntl, mountWithIntl, findTestSubject } from '@kbn/test-jest-helpers';

After

import { render, screen, within } from '@testing-library/react';
import userEvent from '@testing-library/user-event';

Keep @kbn/test-jest-helpers only for non-enzyme utilities (e.g. nextTick, StubBrowserStorage) and RTL render helpers (renderWithKibanaRenderContext, renderWithI18n, renderWithEuiTheme). Remove findTestSubject — use screen.getByTestId instead.

When the component needs i18n or EUI theme context, prefer the RTL helpers from @kbn/test-jest-helpers instead of manually wrapping in providers:

These are drop-in replacements for RTL's render() and accept the same arguments (including renderOptions). When the component needs additional providers (Redux, Router, custom contexts), add them as a wrapper option or inline in JSX.

Rendering

Use screen for queries (queries document.body, so portals are reachable too):

render(<MyComponent />);
expect(screen.getByTestId('foo')).toBeInTheDocument();

Selector migration

Test subject selectors

Note: In Kibana Jest setup, RTL uses testIdAttribute: 'data-test-subj', so getByTestId('x') queries data-test-subj="x" (not data-testid).

Make sure findTestSubject matcher behavior is preserved with a getByTestId RegExp matcher when data-test-subj contains multiple tokens.

After interactions that trigger async updates, prefer findByTestId over getByTestId to avoid act() warnings from unresolved updates.

Kibana-specific fallback: subj() from @kbn/test-subj-selector converts test-subject selector syntax to a CSS selector (supports ~/*/>). Prefer RTL queries first; use this when you truly need CSS selection:

import { subj } from '@kbn/test-subj-selector';

const el = container.querySelector(subj('foo > ~bar'));

Note: Some EUI components reuse the same data-test-subj on both a wrapper and the actual control. If getByTestId throws “Found multiple elements”, use getAllByTestId/queryAllByTestId and narrow (or scope with within(...)) instead of switching to brittle CSS selectors.

CSS selectors

Complex traversals

Enzyme chains like wrapper.find('tbody tr td a').at(3).find('div span').at(2).text() become:

const links = container.querySelectorAll('tbody tr td a');
links[3]?.querySelectorAll('div span')[2]?.textContent;

Global selectors (modals, popovers)

For elements rendered outside the component's container (portals), prefer screen / within(document.body):

// Portal content is in document.body, so screen queries can find it
expect(screen.getByTestId('modal-confirm')).toBeInTheDocument();

// Or scope explicitly
within(document.body).getByTestId('modal-confirm');

Targeting the last element in a NodeList

const items = container.querySelectorAll('.item');
expect(Array.from(items).at(-1)).toHaveTextContent('last');

Assertion migration

Testing component props (mock-based pattern)

When tests assert on props passed to child components, mock the child and inspect mock calls:

jest.mock('@elastic/charts', () => {
  const actual = jest.requireActual('@elastic/charts');
  return {
    ...actual,
    AreaSeries: jest.fn(() => <div data-test-subj="area-series-mock" />),
    Axis: jest.fn(() => <div data-test-subj="axis-mock" />),
  };
});

const MockedAreaSeries = jest.mocked(AreaSeries);
const MockedAxis = jest.mocked(Axis);

it('passes yScaleType to AreaSeries', () => {
  render(<MyChart {...defaultProps} />);
  expect(MockedAreaSeries.mock.calls[0][0].yScaleType).toEqual(configs.series.yScaleType);
});

it('passes tickFormat to xAxis', () => {
  render(<MyChart {...defaultProps} />);
  expect(MockedAxis).toHaveBeenCalledWith(
    expect.objectContaining({ tickFormat: mockTimeFormatter }),
    expect.anything()
  );
});

Use this pattern instead of enzyme's .find(Component).prop('propName'). Clear mocks between tests with jest.clearAllMocks() in beforeEach.

Async & state updates

• Wait for a UI boundary with findBy* (preferred) or waitFor() when you need a custom assertion. Use act() for explicit timer advancement/flush (e.g. jest.runOnlyPendingTimersAsync() in fake-timer suites) or imperative callbacks that trigger React updates.

• Replace wrapper.update() + nextTick() patterns with await waitFor(...).

• For promises that resolve in tests, prefer findByTestId (auto-waits) over getByTestId + waitFor. Prefer reusing the element returned from findBy* instead of re-querying with getBy* immediately after (re-query only when you expect the DOM to change/replace the element).

• For elements that should disappear, prefer waitForElementToBeRemoved(...) (example: await waitForElementToBeRemoved(screen.getByTestId('loading'))).

• Don't wrap fireEvent/userEvent in act(); instead, perform the interaction and then wait on the relevant UI boundary (see bullets above).

• Avoid “fixing” failures by increasing waitFor timeouts; tighten the UI boundary you wait for instead.

Snapshot strategy

• shallow + toMatchSnapshot() → render() + expect(container.children[0]).toMatchSnapshot().
• Snapshots will be larger since RTL renders full DOM. This is expected — do not add mocks just to shrink snapshots during this migration.
• Delete old .snap files and regenerate: yarn test:jest --updateSnapshot <path>.
• Default to container.children[0] snapshots. When the snapshot is too large or noisy, fall back to targeted assertions instead:

expect(screen.getByTestId('chart-title')).toHaveTextContent('Revenue');
expect(screen.getByRole('button', { name: 'Save' })).toBeDisabled();
expect(screen.queryByTestId('error-banner')).not.toBeInTheDocument();

• Portal-based components (popovers, modals, tooltips, toasts) must use targeted assertions, not snapshots. Their panel content renders outside container via portals, so container.children[0] only captures the trigger/anchor — not the actual content. Use screen queries (which search the full document body) or document.querySelector for portals:

// Popover: render with isOpen, assert on panel content via screen
render(
  <MyPopover isOpen button={<button>Toggle</button>}>
    <SelectableList options={options} />
  </MyPopover>
);
expect(screen.getByText('Toggle')).toBeInTheDocument();
expect(screen.getByText('Panel Title')).toBeInTheDocument();
expect(screen.getByText('Option A')).toBeInTheDocument();
expect(document.querySelector('[id^="searchInput"]')).toBeInTheDocument();

// Modal: content renders in a portal, use document.querySelector
expect(document.querySelector('[data-test-subj="confirmModal"]')).toBeInTheDocument();

// Tooltip: content only appears on hover
await userEvent.hover(screen.getByText('Hover me'));
await waitFor(() => {
  expect(screen.getByRole('tooltip')).toHaveTextContent('Tooltip text');
});

Common pitfalls

• Missing providers after removing shallow. Enzyme shallow doesn't render children deeply, hiding missing context providers. After switching to render(), add required providers (I18n, Redux, Router, Theme, etc.) or mock them.
• EUI component explosions. Some EUI components render complex DOM. Mock them if the test doesn't care about their internals. Prefer shared mocks when available (e.g. import "@kbn/code-editor-mock/jest_helper"), then plugin-local __mocks__/ files (e.g. <pluginRoot>/__mocks__/@elastic/charts/index.tsx), then an inline mock factory as a fallback. When stubbing components to <div>s, add a data-test-subj only when the test needs a stable query for "mock rendered".
• Portal-based elements. Modals, toasts, and popovers render outside container. Use document.querySelector or screen (which queries the whole document body). Never snapshot these — use targeted assertions instead (see Snapshot strategy).
• act() warnings. Usually caused by missing await / missing async UI boundary after an interaction. Prefer await screen.findBy... / await waitFor(...) over wrapping events in act() (events are already wrapped). Use act() for explicit timer advancement/flush (e.g. jest.runOnlyPendingTimersAsync() in fake-timer suites) or imperative callbacks that trigger React updates. Never use empty act() blocks (e.g. await act(async () => {})).
• userEvent performance. userEvent simulates full event sequences and scales poorly in CI (geometrically with interaction count). Prefer fireEvent for simple clicks and value changes. Replace userEvent.type(input, 'text') with fireEvent.change(input, { target: { value: 'text' } }) + fireEvent.blur(input) unless the test is specifically exercising per-keystroke behavior (e.g. keydown handlers, typeahead suggestions, input masking/formatting, debounce-on-each-char). When fireEvent.change causes act warnings inside portals/overlays, prefer userEvent.paste over userEvent.type — it sets the full value in one step without per-character overhead.
• Timer-based tests. Replace jest.advanceTimersByTime patterns carefully — RTL's userEvent uses real timers by default. Use userEvent.setup({ advanceTimers: jest.advanceTimersByTime }) when fake timers are needed.

Running tests

yarn test:jest <path-to-test-file> --updateSnapshot

Checklist

• All enzyme imports removed
• All shallow() / mount() replaced with render()
• shallowWithIntl / mountWithIntl replaced with render() + I18nProvider wrapper
• findTestSubject replaced with equivalent selector semantics (exact vs token ~= match)
• Selectors migrated to RTL queries or container.querySelector
• .simulate() replaced with userEvent or fireEvent
• .prop() / .props() replaced with mock-based pattern
• Snapshots regenerated
• Dead tests (passing only due to shallow rendering) removed
• Test passes: yarn test:jest <path>

References

• Migrate from Enzyme | Testing Library