Add .registerAlias() Test

test/api/registerAlias.js

@@ -0,0 +1,24 @@
+'use strict';
+
+const hljs   = require('../../build');
+const should = require('should');
+
+describe('.registerAlias()', () => {
+  it('should get an existing language by alias', () => {
+    hljs.registerAlias('jquery', {
+      languageName: 'javascript'
+    });
+    const result = hljs.getLanguage('jquery');
+
+    result.should.be.instanceOf(Object);
+  });
+
+  it('should get an existing language by aliases', () => {
+    hljs.registerAlias(['jquery', 'jqueryui'], {
+      languageName: 'javascript'
+    });
+    const result = hljs.getLanguage('jquery');
+
+    result.should.be.instanceOf(Object);
+  });
+});