Return new expect based on another expect. All definitions are deep merged. Duplicate fields will be replaced by the new definition.

import {
  expect,
  extendExpect,
  test,
  toBeString,
} from "https://deno.land/x/unitest@$VERSION/mod.ts";

const newExpect = extendExpect(expect, {
  matcherMap: {
    toBeString,
  },
});

test("should be string", () => {
  newExpect("unitest").toBeString();
});