anchor.diff:         "pconf":   null,
          "proot":   null,
          "iconf":   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) {
  +  } catch (e, s) {
       // Unexpected error calling runDart or parsing the result.
       // Report it and continue.
       print("ERROR running $name: $e\n$s");
  
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:   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",
  