"jest": {
    "moduleNameMapper": {
      "\.(css|less)$": "identity-obj-proxy"
    },
    "transform": {
      "^.+\.tsx?$": "<rootDir>/node_modules/ts-jest/preprocessor.js",
      "\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$": "<rootDir>/fileMock.js"
    },
    "testRegex": "\.(test|spec)\.tsx?$",
    "moduleFileExtensions": [
      "ts",
      "tsx",
      "js",
      "jsx",
      "json"
    ]
  }

import * as styles from './Foo.less';
import myImg from './myImg.png';

export const Foo = () => (
  <div
    className="something"
    style={{backgroundImage: `url(${myImg})`}}
  >
  Some content
  </div>
);

import * as React from 'react';
import { shallow } from 'enzyme';
import { Foo } from './Foo';

test('Foo has myImg in style prop', () => {
  const wrapper = shallow(
    <Foo />
  );
  expect(wrapper.find('.something').prop('style')).toContain('myImg.png');
});

expect(object).toContain(value)

Expected object:
  {"backgroundImage": "url(undefined)"}
To contain value:
  "myImg.png"