anchor.diff:    await test("http: no resolution", "%http/main.dart",
       http: {"main": testMain},
       expect: {
  +      "iroot": "%http/packages/",
         // "foo": null,
         "foo/": "%http/packages/foo/",
         "foo/bar": "%http/packages/foo/bar",
  
positive.code: 
  import "dart:async";
  import "dart:io";
  import "dart:isolate";
  import "dart:convert" show JSON;
  import "package:path/path.dart" as p;
  import "package:expect/expect.dart";
  import "package:async_helper/async_helper.dart";
  
  main() async {
  
negative.code:        "pconf":   null,
         "proot":   null,
         "iconf":   null,
         "iroot":   null,
         // "foo":   null,
         "foo/":    null,
         "foo/bar": null,
         "foo.x":  "qux",
      }..addAll(expect);
      match(JSON.decode(output), expects, fixPaths, name);
    } catch (e, s) {
      // Unexpected error calling runDart or parsing the result.
      // Report it and continue.
      print("ERROR running $name: $e\n$s");
  