new_contents: import contextlib
  import json
  import os
  
  from nose.tools import istest, assert_equal
  
  from whack.tempdir import create_temporary_dir
  from whack.files import sh_script_description, plain_file, read_file
  from whack.sources import PackageSource
  from whack.builder import build
      
  
  @istest
  def build_uses_params_as_environment_variables_in_build():
      with _package_source("echo $VERSION > $1/version", {}) as package_source:
          with create_temporary_dir() as target_dir:
              build(package_source, {"version": "42"}, target_dir)
              assert_equal("42\n", read_file(os.path.join(target_dir, "version")))
  
  
  @contextlib.contextmanager
  def _package_source(build_script, description):
      files = [
          plain_file("whack/whack.json", json.dumps(description)),
          sh_script_description("whack/build", build_script),
      ]
      with create_temporary_dir(files) as package_source_dir:
          yield PackageSource(package_source_dir)
          
  
subject: Add basic test for build