text: const acorn = require('acorn');
  
  const modules = {
  	main: "import foo from 'foo';\nfoo();",
  
  	// the code points to './bar' but the AST points to './baz', so we
  	// can check the AST is being used
  	foo: {
  		code: "import bar from 'bar';\nexport default function foo () {\n\tassert.equal(bar, 42);\n}",
  		ast: acorn.parse(
  			"import bar from 'baz';\nexport default function foo () {\n\tassert.equal(bar, 42);\n}",
  			{
  				ecmaVersion: 6,
  				sourceType: 'module'
  			}
  		)
  	},
  
  	baz: 'export default 42;'
  };
  
  module.exports = {
  	description: 'uses supplied AST',
  	options: {
  		plugins: [
  			{
  				resolveId(importee, importer) {
  					if (!importer) return 'main';
  					return importee;
  				},
  				load(id) {
  					if (id === 'bar') {
  						throw new Error('loaded incorrect module');
  					}
  
  					return modules[id];
  				}
  			}
  		]
  	}
  };
  