anchor.diff:      this.port,
       this.dillFilePath,
     }) : assert(shellPath != null) {
  +
  +    // Compiler maintains and updates single incremental dill file.
  +    // Incremental compilation requests done for each test copy that file away
  +    // for independent execution.
  +    final Directory outputDillDirectory = fs.systemTempDirectory
  +        .createTempSync('output_dill');
  +    final File outputDill = outputDillDirectory.childFile('output.dill');
  +
       compilerController.stream.listen((CompilationRequest request) async {
         final bool isEmpty = compilationQueue.isEmpty;
         compilationQueue.add(request);
  
positive.code:           compilationQueue.removeAt(0);
          }
        }
      });
    }
  
  
negative.code:           final CompilationRequest request = compilationQueue.first;
            printTrace('Compiling ${request.path}');
            final String outputPath = await compiler.recompile(request.path,
              <String>[request.path],
              outputPath: outputDill.path
            );
            // Copy output dill next to the source file.
            await outputDill.copy(request.path + '.dill');
            compiler.accept();
            compiler.reset();
            request.result.complete(outputPath);
  