code: def testInvalidFrequency(self):
      with self.assertRaisesRegexp(Exception, "Invalid frequency.*"):
          yahoofeed.Feed(frequency=bar.Frequency.MINUTE)
  
imports: import datetime
  from .None import common
  from .None import barfeed_test
  from .None import feed_test
  from pyalgotrade.utils import dt
  from pyalgotrade.barfeed import yahoofeed
  from pyalgotrade.barfeed import csvfeed
  from pyalgotrade import bar
  from pyalgotrade import marketsession
label_desc: Use image node_id 6 for calling the FeedTestCase obj's underlying member method code with example usage: obj.testInvalidFrequency() without return types