more isolated test

.babelrc

{
  "plugins": ["syntax-class-properties", "../../../../../src/babel"]
}

actual.js

class Foo {
  bar = (a, b) => {
    return a(b);
  };
}

expected.js

var _this = this;

class Foo {
  bar = (...params) => _this.__bar__REACT_HOT_LOADER__(...params);

  __bar__REACT_HOT_LOADER__(a, b) {
    return a(b);
  }

}
;

(function () {
  if (typeof __REACT_HOT_LOADER__ === 'undefined') {
    return;
  }

  __REACT_HOT_LOADER__.register(Foo, "Foo", __FILENAME__);
})();

;