Edit the data-es5.js, data-es6.js, data-es7.js, or data-non-standard.js files to adjust the tests and their recorded browser results. Run node build.js to build the HTML files from these JavaScript sources.
The ES6 tests themselves should be written in pure ES3, except for the sole ES6 feature being tested (as well as any ES5 features strictly required to use the ES6 feature). The test code is placed in multi-line comments (as in this hack), so that Node/io.js can parse the data scripts without throwing syntax errors when encountering features it does not support. The build.js script will wrap the code in an eval call inside a try, so the tests themselves do not need to catch errors that non-supporting platforms may throw.
The ES6 tests have a significance rating, which affects how a platform's total support percentage is calculated. A test rated "large" (representing a landmark, transformative feature) is worth 1, one rated "medium" (representing a significant feature that's less universally useful, or is primarily connected to another feature) is worth 0.5, and one rated "small" (representing a useful but subtle improvement from ES5) is worth 0.25.
Run npm install to install the compilers under test (and remember to npm update them frequently).
Then run node build.js compilers to create compiler test pages under es6/compilers. Currently only the ES6 tests produce compiler test pages.
Open the compilers' HTML files in a browser with close to zero native ES6 support, such as Internet Explorer 9 (although its lack of support for strict mode will cause some tests to fail), Opera 12, or Safari 5.1 (bearing in mind their native support for TypedArrays, __proto__ and such).
Note that some tests cannot be compiled correctly, as they rely on runtime eval() results to ensure that, for instance, certain syntactic constructs are syntax errors. These will fail on the compiler test pages. Support for those features should be divined manually.