old_contents: import React from 'react';
  import { mount } from 'enzyme';
  
  import ThemeProvider from '../src/ThemeProvider';
  import Overlay from '../src/Overlay';
  import Popover from '../src/Popover';
  
  describe('usePopperMarginModifiers', () => {
    it('Should set arrow margin to 0px with prefixed popover and dropdown-menu', () => {
      const wrapper = mount(
        <ThemeProvider prefixes={{ popover: 'prefixed' }}>
          <Overlay show>
            <Popover id="test-popover" />
          </Overlay>
        </ThemeProvider>,
      );
  
      const margin = wrapper.find('.arrow').getDOMNode().style.margin;
      assert.equal(margin, '0px');
    });
  });
  
new_contents: import React from 'react';
  import { mount } from 'enzyme';
  
  import ThemeProvider from '../src/ThemeProvider';
  import Overlay from '../src/Overlay';
  import Popover from '../src/Popover';
  
  describe('usePopperMarginModifiers', () => {
    it('Should set arrow margin to 0px with prefixed popover and dropdown-menu', () => {
      const wrapper = mount(
        <ThemeProvider prefixes={{ popover: 'prefixed' }}>
          <Overlay show>
            <Popover id="test-popover" />
          </Overlay>
        </ThemeProvider>,
      );
  
      const margin = wrapper.find('.popover-arrow').getDOMNode().style.margin;
      assert.equal(margin, '0px');
    });
  });
  
subject: Fix failing popover tests