var actual = transform(
  'var x = <sometag />',
  Object.assign({}, opts, { filename: '/fake/path/mock.js' })
).code;

var expected = `
var _jsxFileName = "/fake/path/mock.js";
var x = <sometag __source={{
  fileName: _jsxFileName,
  lineNumber: 1,
  columnNumber: 9
}} />;
`.trim();

expect(actual).toBe(expected);