Module mapper and custom toJson for bemified CSS modules (see https://medium.com/trabe/using-bem-conventions-in-css-modules-leveraging-custom-webpack-loaders-fd985f72bcb2)

bem-proxy.js

const hyphenize = s => s.replace(/([A-Z])/g, g => `-${g[0].toLowerCase()}`);

const classify = (block, element, modifier) => {
  const parts = [hyphenize(block)];

  if (element) {
    parts.push("__");
    parts.push(hyphenize(element));
  }

  if (modifier) {
    parts.push("--");
    parts.push(hyphenize(modifier.slice(1)));
  }

  return parts.join("");
};

const blockProxy = block =>
  new Proxy(
    { cssModule: true },
    {
      get: (target, key) => {
        if (key === "hasOwnProperty") {
          return prop => prop === "toString";
        }

        if (key === "toString" || key === Symbol.toPrimitive) {
          return () => classify(block);
        }

        if (key.match(/^\$/)) {
          const modifier = key;
          return modifierProxy(block, undefined, modifier);
        }

        const element = key;
        return elementProxy(block, element);
      },
    },
  );

const elementProxy = (block, element) =>
  new Proxy(
    { cssModule: true },
    {
      get: (target, key) => {
        if (key === "hasOwnProperty") {
          return prop => prop === "toString";
        }

        if (key === "toString" || key === Symbol.toPrimitive) {
          return () => classify(block, element);
        }
        const modifier = key;
        return modifierProxy(block, element, modifier);
      },
    },
  );

const modifierProxy = (block, element, modifier) => ({
  cssModule: true,
  toString: () => classify(block, element, modifier),
});

export default new Proxy(
  {},
  {
    get: (_, block) => blockProxy(block),
  },
);

custom-to-json.js

import enzymeToJons from "enzyme-to-json"; 

const fixCSSmodules = info => {
  if (info.props && info.props.className && info.props.className.cssModule) {
    info.props.className = info.props.className.toString();
  }
  return info;
};

export const toJson = (wrapper, options) =>
  enzymeToJson(wrapper, {
    map: fixCSSmodules,
    ...options,
  });