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node_modules/mocha/lib/esm-utils.js

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+const path = require('path');
+const url = require('url');
+
+const formattedImport = async file => {
+  if (path.isAbsolute(file)) {
+    try {
+      return await import(url.pathToFileURL(file));
+    } catch (err) {
+      // This is a hack created because ESM in Node.js (at least in Node v15.5.1) does not emit
+      // the location of the syntax error in the error thrown.
+      // This is problematic because the user can't see what file has the problem,
+      // so we add the file location to the error.
+      // This `if` should be removed once Node.js fixes the problem.
+      if (
+        err instanceof SyntaxError &&
+        err.message &&
+        err.stack &&
+        !err.stack.includes(file)
+      ) {
+        const newErrorWithFilename = new SyntaxError(err.message);
+        newErrorWithFilename.stack = err.stack.replace(
+          /^SyntaxError/,
+          `SyntaxError[ @${file} ]`
+        );
+        throw newErrorWithFilename;
+      }
+      throw err;
+    }
+  }
+  return import(file);
+};
+
+exports.requireOrImport = async file => {
+  if (path.extname(file) === '.mjs') {
+    return formattedImport(file);
+  }
+  // This is currently the only known way of figuring out whether a file is CJS or ESM.
+  // If Node.js or the community establish a better procedure for that, we can fix this code.
+  // Another option here would be to always use `import()`, as this also supports CJS, but I would be
+  // wary of using it for _all_ existing test files, till ESM is fully stable.
+  try {
+    return require(file);
+  } catch (err) {
+    if (err.code === 'ERR_REQUIRE_ESM') {
+      return formattedImport(file);
+    } else {
+      throw err;
+    }
+  }
+};
+
+exports.loadFilesAsync = async (files, preLoadFunc, postLoadFunc) => {
+  for (const file of files) {
+    preLoadFunc(file);
+    const result = await exports.requireOrImport(path.resolve(file));
+    postLoadFunc(file, result);
+  }
+};