import type { TypeMatcher } from './matcher';
/**
 * Match any number.
 *
 * @example
 * const fn = mock<(x: number) => number>();
 * when(() => fn(It.isNumber())).returns(42);
 *
 * fn(20.5) === 42
 * fn(NaN) // throws
 */
export declare const isNumber: () => TypeMatcher<number>;