Testing rrules

mylog_rrule.jl

using ChainRulesCore, ChainRulesTestUtils, Test

function mylog(x::Real)
    r = log(abs(x))
    if x > 0
        return r
    else
        return oftype(r, -Inf)
    end
end

function ChainRulesCore.rrule(::typeof(mylog), x)
    function mylog_pullback(δ)
        if x > 0
            dx = 1/x
        else
            dx = oftype(1/x, Inf)
        end
        return NoTangent(), dx
    end
    return mylog(x), mylog_pullback
end

test_rrule(mylog, 1.0)