test: repro #5175

.eslintignore

@@ -2,3 +2,4 @@ docs/
 bin/
 test/triage/
 test/model.discriminator.test.js
+test/es6/

test/es6.test.js

@@ -0,0 +1,5 @@
+'use strict';
+
+if (parseInt(process.versions.node.split('.')[0], 10) >= 4) {
+  require('./es6/all.test.es6.js');
+}

test/es6/all.test.es6.js

@@ -0,0 +1,28 @@
+'use strict';
+
+/**
+ * Module dependencies.
+ */
+
+const assert = require('assert');
+const start = require('../common');
+
+const mongoose = start.mongoose;
+
+describe('bug fixes', function() {
+  let db;
+
+  before(function() {
+    db = start();
+  });
+
+  it('discriminators with classes modifies class in place (gh-5175)', function(done) {
+    class Vehicle extends mongoose.Model { }
+    var V = mongoose.model(Vehicle, new mongoose.Schema());
+    assert.ok(V === Vehicle);
+    class Car extends Vehicle { }
+    var C = Vehicle.discriminator(Car, new mongoose.Schema());
+    assert.ok(C === Car);
+    done();
+  });
+});