Efficient use of test or assert

[jw3126]

• @test is very slow and for tests.
• @assert is for double-checking invariants you are certaint are true. The only way it can fire, is when there are bugs in the program. E.g.

# good
y = _my_fast_sum_of_squares(xs)
@assert y >= 0

# bad
function public_api(x)
    @assert x >= 0
end

• ArgCheck.jl is specifically designed for fast argument checks with nice error messages.