NEW YORK ( TheStreet) -- Investors need to challenge their own ideas, Jim Cramer told the viewers of his "Mad Money" TV show Friday. That's why his game plan for next week includes using the latest data to confirm or disprove many of his current investment theses. Cramer said the latest retail sales numbers will be released on Tuesday. He said that while these numbers are interesting in a broad sense, he's focusing on the earnings of electronics giant Best Buy ( BBY). "There's no better test of the consumer than seeing if they're buying stuff they really don't need," said Cramer, adding that's why Best Buy is a great test of whether the back-to-school" shopping season is on track.