    // Both sd and ce are supported, force both polyfills
    if (flags.length === 2) {
      // ce + sd becomes a single test iteration.
      flags.push('wc-ce=true&wc-shadydom=true');
    }

    // economize testing by testing css shimming
    // only against 1 environment (native or polyfill).
    if (window.CSS && CSS.supports && CSS.supports('box-shadow', '0 0 0 var(--foo)')) {
      // Note: Disabled to speed up testing, may be reenabled at a later date when the test timing is less of an issue.
     