Numeric less-than assertion
Passes if a < b for numeric arguments (Int or Float).
Returns Expect_hold when either argument is NA;
Expect_stop on errors.
a (Int): | Float The left-hand
numeric value.
b (Int): | Float The right-hand
numeric value.
Expect_pass when a < b,
Expect_stop otherwise.
assert(expect_lt(1, 2))
assert(expect_lt(1.5, 2.5))