How can I mock a function called by the function I am exercising? The functions are in the same file

Question

The file I am writing tests for is exporting the following

module.exports = {
  groupProducts,
  test: {
    getNow,
  },
};

I know how to mock getNow when I am calling it from my test:

describe('groupProducts', () => {
  it('groups productInfo ids into today or future date groups', () => {
    // Arrange
    const expectedResult = {};
    const nowSpy = jest.spyOn(test, 'getNow').mockReturnValue(dayjs('2001-02-03T04:05:06.007Z'));

    // Act
    const dateToIds = groupProducts(productInfos, test.getNow());

    // Expect
    expect(dateToIds).toEqual(expectedResult);

    // Restore
    nowSpy.mockRestore();
  });
});

But how do I mock getNow when it is called from the exercised function and not from the test?

describe('groupProducts', () => {
  it('groups productInfo ids into today or future date groups', () => {
    // Arrange
    const expectedResult = {};
    const nowSpy = jest.spyOn(test, 'getNow').mockReturnValue(dayjs('2001-02-03T04:05:06.007Z'));

    // Act
    const dateToIds = groupProducts(productInfos);

    // Expect
    expect(dateToIds).toEqual(expectedResult);

    // Restore
    nowSpy.mockRestore();
  });
});

groupProducts calls real getNow. The spy doesn't work as I had intended.