anchor.diff:        testMatrix["builder_configurations"] as List<dynamic>;
     // Determine what named configuration to run and which builders to download
     // existing results from.
  -  ResolvedConfigurations configurations = resolveNamedConfigurations(
  +  final testedConfigurations = resolveNamedConfigurations(
         branches,
         buildersConfigurations,
         options["branch"],
         requestedNamedConfigurations,
         requestedBuilder);
  -  if (configurations == null) {
  +  if (testedConfigurations == null) {
       // No valid configuration could be found. The error has already been
  -    // reported by [resolveConfiguration].
  +    // reported by [resolveConfigurations].
       exitCode = 1;
       return;
     }
  -  Set<String> namedConfigurations = configurations.configurationNames;
  +  final namedConfigurations = testedConfigurations.keys.toSet();
  +  final builders =
  +      testedConfigurations.values.expand((builders) => builders).toSet();
     // Print information about the resolved builders to compare with.
  -  for (final builder in configurations.builders) {
  +  for (final namedConfiguration in namedConfigurations) {
  +    final testedBuilders = testedConfigurations[namedConfiguration];
  +    final onWhichBuilders = testedBuilders.length == 1
  +        ? "builder ${testedBuilders.single}"
  +        : "builders${testedBuilders.map((b) => "\n  $b").join()}";
       if (localConfiguration != null) {
  -      print("Testing the named configuration $localConfiguration "
  -          "compared with builder $builder's configuration "
  -          "${namedConfigurations.single}");
  +      print("Testing named configuration $localConfiguration "
  +          "compared with configuration ${namedConfiguration} "
  +          "on $onWhichBuilders");
       } else {
  -      print("Testing the named configuration(s) "
  -          "${namedConfigurations.join(",")} "
  -          "compared with builder $builder");
  +      print("Testing named configuration $namedConfiguration "
  +          "compared with $onWhichBuilders");
       }
     }
     // Use given commit or find out where the current HEAD branched.
  
positive.code:     final tasks = <Future>[];
      bool needsConfigurationOverride = localConfiguration != null &&
          localConfiguration != namedConfigurations.single;
      bool needsMerge = configurations.builders.length > 1;
      final inexactBuilds = <String, String>{};
      var previousFileName = "previous.json";
      var flakyFileName = "flaky.json";
      var downloadNumber = 0;
      // Download the previous results and flakiness info from cloud storage.
      for (final builder in configurations.builders) {
        if (needsMerge) {
          previousFileName = "previous-$downloadNumber.json";
          flakyFileName = "flaky-$downloadNumber.json";
  
negative.code:       orElse: () => "master");
  }
  
  /// Finds the named configuration to test according to the test matrix
  /// information and the command line options.
  Map<String, Set<String>> resolveNamedConfigurations(
      List<String> branches,
      List<dynamic> buildersConfigurations,
      String requestedBranch,
      List<String> requestedNamedConfigurations,
      String requestedBuilder) {
    final testedConfigurations = <String, Set<String>>{};
    var foundBuilder = false;
    for (final builderConfiguration in buildersConfigurations) {
      for (final builder in builderConfiguration["builders"]) {
        if (requestedBuilder != null && builder != requestedBuilder) {
  