CLN: Deprecation of assert_

#7131: Run s/self.assert_(/self.assertTrue( on remaining instances I can find. These were the multi-line expressions, and I tried to retain the formatting of the expressions
CLN: Deprecation of assert_

Fix formatting of one multi-line assertion, from assert_ --> assertTrue cleanup
Merge pull request #7172 from bwignall/issue7131_assert_

CLN: Deprecation of assert_