restore and deprecate lookupFiles() in lib/utils

lookupFiles() broke (moved) in version v8.1.0, this returns it and issues a soft deprecation warning.
in the browser, this function should not be called, but if it is, an `ERR_MOCHA_UNSUPPORTED` `Error` is thrown

lib/utils.js

@@ -645,3 +645,32 @@ exports.cwd = function cwd() {
 exports.isBrowser = function isBrowser() {
   return Boolean(process.browser);
 };
+
+/**
+ * Lookup file names at the given `path`.
+ *
+ * @description
+ * Filenames are returned in _traversal_ order by the OS/filesystem.
+ * **Make no assumption that the names will be sorted in any fashion.**
+ *
+ * @public
+ * @alias module:lib/cli.lookupFiles
+ * @param {string} filepath - Base path to start searching from.
+ * @param {string[]} [extensions=[]] - File extensions to look for.
+ * @param {boolean} [recursive=false] - Whether to recurse into subdirectories.
+ * @return {string[]} An array of paths.
+ * @throws {Error} if no files match pattern.
+ * @throws {TypeError} if `filepath` is directory and `extensions` not provided.
+ * @deprecated Moved to {@link module:lib/cli.lookupFiles}
+ */
+exports.lookupFiles = (...args) => {
+  if (exports.isBrowser()) {
+    throw require('./errors').createUnsupportedError(
+      'lookupFiles() is only supported in Node.js!'
+    );
+  }
+  exports.deprecate(
+    '`lookupFiles()` in module `mocha/lib/utils` has moved to module `mocha/lib/cli` and will be removed in the next major revision of Mocha'
+  );
+  return require('./cli').lookupFiles(...args);
+};

package.json

@@ -173,7 +173,8 @@
     "./lib/nodejs/worker.js": false,
     "./lib/nodejs/buffered-worker-pool.js": false,
     "./lib/nodejs/parallel-buffered-runner.js": false,
-    "./lib/nodejs/reporters/parallel-buffered.js": false
+    "./lib/nodejs/reporters/parallel-buffered.js": false,
+    "./lib/cli/index.js": false
   },
   "prettier": {
     "singleQuote": true,

test/unit/utils.spec.js

@@ -742,4 +742,49 @@ describe('lib/utils', function() {
       expect(utils.slug('poppies & fritz'), 'to be', 'poppies-fritz');
     });
   });
+
+  describe('lookupFiles()', function() {
+    beforeEach(function() {
+      sinon.stub(utils, 'deprecate');
+    });
+
+    describe('when run in Node.js', function() {
+      before(function() {
+        if (process.browser) {
+          return this.skip();
+        }
+      });
+
+      beforeEach(function() {
+        sinon.stub(utils, 'isBrowser').returns(false);
+        sinon.stub(require('../../lib/cli'), 'lookupFiles').returns([]);
+      });
+
+      it('should print a deprecation message', function() {
+        utils.lookupFiles();
+        expect(utils.deprecate, 'was called once');
+      });
+
+      it('should delegate to new location of lookupFiles()', function() {
+        utils.lookupFiles(['foo']);
+        expect(
+          require('../../lib/cli').lookupFiles,
+          'to have a call satisfying',
+          [['foo']]
+        ).and('was called once');
+      });
+    });
+
+    describe('when run in browser', function() {
+      beforeEach(function() {
+        sinon.stub(utils, 'isBrowser').returns(true);
+      });
+
+      it('should throw', function() {
+        expect(() => utils.lookupFiles(['foo']), 'to throw', {
+          code: 'ERR_MOCHA_UNSUPPORTED'
+        });
+      });
+    });
+  });
 });