Loose falsiness assertion
Passes if x is falsy per is_truthy
(0, false, VNullNode, empty
containers, etc.). NA produces Expect_hold.
Any): The value to check.Expect_pass when x is falsy;
Expect_hold on NA; Expect_stop on errors or
truthy values.
assert(expect_falsy(0))
assert(expect_falsy(false))