This page has older versions of Mocha and Chai in order to work with old browsers like IE. It also includes Babel in case someone writes tests that aren't ES5 compatible. Babel and its polyfills only apply to the test code itself. Cytoscape is built using Babel and Cytoscape uses its own internal polyfills where necessary. Running Babel in old browsers like IE is very slow, so please be patient.
If you are running these tests in a slow VM, some of the style-related tests may fail. Those tests are timing-dependent, and old browsers may not support requestAnimationFrame(). Refresh and try again if you get a style test failure, or click a section to run only the failing subset of tests.