setupTests.js

import React from "react";
import "@testing-library/jest-dom/extend-expect";
import { loadEnvConfig } from "@next/env";

const projectDir = process.cwd();
loadEnvConfig(projectDir, undefined, { info: () => {}, error: () => {} });

const hasChildren = (node) =>
  node && (node.children || (node.props && node.props.children));

const getChildren = (node) =>
  node && node.children ? node.children : node.props && node.props.children;

const renderNodes = (reactNodes) => {
  if (typeof reactNodes === "string") {
    return reactNodes;
  }

  return Object.keys(reactNodes).map((key, i) => {
    const child = reactNodes[key];
    const isElement = React.isValidElement(child);

    if (typeof child === "string") {
      return child;
    }
    if (hasChildren(child)) {
      const inner = renderNodes(getChildren(child));
      return React.cloneElement(child, { ...child.props, key: i }, inner);
    }
    if (typeof child === "object" && !isElement) {
      return Object.keys(child).reduce(
        (str, childKey) => `${str}${child[childKey]}`,
        ""
      );
    }

    return child;
  });
};

jest.mock("react-i18next", () => ({
  useTranslation: () => {
    return {
      t: (str) => str,
      i18n: {
        changeLanguage: () => new Promise(() => {}),
      },
    };
  },
  Trans: ({ children }) =>
    Array.isArray(children) ? renderNodes(children) : renderNodes([children]),
}));