fix --ui issues, closes #3746

lib/mocha.js

@@ -260,25 +260,30 @@ Mocha.prototype.reporter = function(reporter, reporterOptions) {
  * @public
  * @see {@link https://mochajs.org/#-u---ui-name|CLI option}
  * @see {@link https://mochajs.org/#interfaces|Interface DSLs}
- * @param {string} [name=bdd] - Interface name.
+ * @param {string|Function} [ui=bdd] - Interface name or class.
  * @returns {Mocha} this
  * @chainable
  * @throws {Error} if requested interface cannot be loaded
  */
-Mocha.prototype.ui = function(name) {
-  name = name || 'bdd';
-  this._ui = exports.interfaces[name];
-  if (!this._ui) {
-    try {
-      this._ui = require(name);
-    } catch (err) {
-      throw createInvalidInterfaceError(
-        'invalid interface ' + sQuote(name),
-        name
-      );
+Mocha.prototype.ui = function(ui) {
+  var bindInterface;
+  if (typeof ui === 'function') {
+    bindInterface = ui;
+  } else {
+    ui = ui || 'bdd';
+    bindInterface = exports.interfaces[ui];
+    if (!bindInterface) {
+      try {
+        bindInterface = require(ui);
+      } catch (err) {
+        throw createInvalidInterfaceError(
+          'invalid interface ' + sQuote(ui),
+          ui
+        );
+      }
     }
   }
-  this._ui = this._ui(this.suite);
+  bindInterface(this.suite);
 
   this.suite.on(EVENT_FILE_PRE_REQUIRE, function(context) {
     exports.afterEach = context.afterEach || context.teardown;

test/integration/fixtures/regression/1794/simple-ui.fixture.js → test/integration/fixtures/simple-ui.fixture.js

@@ -1,6 +1,6 @@
 'use strict';
 
-var Mocha = require('../../../../../lib/mocha');
+var Mocha = require('../../../lib/mocha');
 var Test = Mocha.Test;
 var EVENT_FILE_PRE_REQUIRE = Mocha.Suite.constants.EVENT_FILE_PRE_REQUIRE;
 
@@ -13,7 +13,7 @@ module.exports = Mocha.interfaces['simple-ui'] = function(suite) {
     file,
     mocha
   ) {
-    var common = require('../../../../../lib/interfaces/common')(
+    var common = require('../../../lib/interfaces/common')(
       [suite],
       context
     );

test/integration/options/ui.spec.js

@@ -0,0 +1,34 @@
+'use strict';
+
+var helpers = require('../helpers');
+var runMocha = helpers.runMocha;
+
+describe('--ui', function() {
+  var simpleUiPath = require.resolve('../fixtures/simple-ui.fixture');
+
+  it('should load interface and run it', function(done) {
+    runMocha('test-for-simple-ui', ['--ui', simpleUiPath], function(err, res) {
+      if (err) {
+        done(err);
+        return;
+      }
+      expect(res, 'to have passed');
+      done();
+    });
+  });
+
+  it("should work if required and name added to Mocha's `interfaces` prop", function(done) {
+    runMocha(
+      'test-for-simple-ui',
+      ['--require', simpleUiPath, '--ui', 'simple-ui'],
+      function(err, res) {
+        if (err) {
+          done(err);
+          return;
+        }
+        expect(res, 'to have passed');
+        done();
+      }
+    );
+  });
+});

test/integration/regression.spec.js

@@ -1,6 +1,5 @@
 'use strict';
 
-var path = require('path');
 var run = require('./helpers').runMocha;
 var runJSON = require('./helpers').runMochaJSON;
 
@@ -25,25 +24,6 @@ describe('regressions', function() {
     });
   });
 
-  it("issue-1794: Can't --require custom UI and use it", function(done) {
-    var simpleUiPath = path.join(
-      __dirname,
-      'fixtures',
-      'regression',
-      '1794',
-      'simple-ui.fixture.js'
-    );
-    var args = ['--require', simpleUiPath, '--ui', 'simple-ui'];
-    run('regression/1794/issue-1794.fixture.js', args, function(err, res) {
-      if (err) {
-        done(err);
-        return;
-      }
-      expect(res, 'to have passed');
-      done();
-    });
-  });
-
   it('issue-1991: Declarations do not get cleaned up unless you set them to `null` - Memory Leak', function(done) {
     // on a modern MBP takes ±5 seconds on node 4.0, but on older laptops with node 0.12 ±40 seconds.
     // Could easily take longer on even weaker machines (Travis-CI containers for example).