/**
 * Mock the ResizeObserver to be able to test components that use a resize
 * observer (e.g. useMeasure, useContainerBreakpoints, and components that
 * use them like BaseInput). Recommended for all React libs.
 *
 * Implementation note: under Vitest the mock was a single
 * `vi.fn().mockImplementation(...)` so callers could:
 *   1. `new global.ResizeObserver(cb)` from the SUT (the implementation
 *      function is callable with `new` because it's a `function` expression
 *      which has a working `[[Construct]]` slot), AND
 *   2. `(global.ResizeObserver as Mock).mockImplementation(...)` from the
 *      spec to capture the callback / inspect constructor arguments.
 *
 * Vitest 4's `vi.fn()` is also constructable when the impl is a `function`
 * expression (arrow functions are *not* constructable), so we keep the
 * same shape - this preserves both call sites that the migration would
 * otherwise have to rewrite.
 */
export declare const setupResizeObserver: () => void;