code: function wantsStage4(userOptions, projectDir) {
  	if (!userOptions) {
  		return false;
  	}
  
  	if (!userOptions.testOptions.presets) {
  		return true;
  	}
  
  	const stage4 = require('../stage-4');
  	return userOptions.testOptions.presets.every(arr => {
  		if (!Array.isArray(arr)) {
  			return true; // There aren't any preset options.
  		}
  
  		const [ref, options] = arr;
  		// Require the preset given the aliasing `ava/stage-4` does towards
  		// `@ava/babel-preset-stage-4`.
  		const resolved = require(babel.resolvePreset(ref, projectDir));
  		return resolved !== stage4 || options !== false;
  	});
  }
docs: Assume the stage-4 preset is wanted if there are `userOptions`, but there is no declaration of a stage-` preset that comes with `false` for its options.  Ideally we'd detect the stage-4 preset anywhere in the configuration hierarchy, but Babel's loadPartialConfig() does not return disabled presets. See <https://github.com/babel/babel/issues/7920>.