The replacement of assert_ with assertTrue [1] resulted in a number of
tests using calls of the form assertTrue(not <condition>). This patch
replaces those with assertFalse(<condition>).
[1] change I74705c6498249337bfdf955d62e0ad972035bc1f
Change-Id: I78b49558f4425c2335df187b1793d1e4b3c514b1