fail();
        }
        throw new SomeError();
      }
    };
  }

  // TODO(cpovirk): top-level class?
  static class ExecutorSpy implements Executor {

    Executor delegate;
    boolean wasExecuted;

    public ExecutorSpy(Executor delegate) {
      this.delegate = delegate;
    }

    @Override
    public void execute(Runnable command) {
      delegate.execute(command);

          fail();
        }
        throw new SomeError();
      }
    };
  }

  // TODO(cpovirk): top-level class?
  static class ExecutorSpy implements Executor {

    Executor delegate;
    boolean wasExecuted;

    public ExecutorSpy(Executor delegate) {
      this.delegate = delegate;
    }

    @Override
    public void execute(Runnable command) {
      delegate.execute(command);