Use .debug to output debug info to console with console.debug.

import {
  debug,
  defineExpect,
  jestExtendedMatcherMap,
  test,
} from "https://deno.land/x/unitest@$VERSION/mod.ts";

test("should output debug info", () => {
  const expect = defineExpect({
    matcherMap: jestExtendedMatcherMap,
    modifierMap: {
      debug,
    },
  });
  expect("Deno").debug.toBeString();

  // Output to console:
  // DEBUG { Context }
});