How to I test both generated and non-generated implementation paths of a function that uses if @generated? I’m sure I saw something about it once, but I can’t find it again …
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Have you found an answer to this? I’d want to know the same thing.
No, no solution yet, it seems. 
The language itself must have some testing of the @generated macro. According to git blame @jeff.bezanson wrote the if @generated functionality into the language. He might have some insight. In the mean time I’ll see if I can find some unit tests in base.
I also opened https://github.com/JuliaLang/julia/issues/38394
Here is my attempt at a solution:
julia> f(x, y) = @generated() ? :x : y
f (generic function with 1 method)
julia> function _invoke(f, x...; generated)
ci = code_lowered(f, Core.Typeof(x); generated)[1]
g = @eval @generated function g($([gensym() for _ in x]...))
return $(QuoteNode(ci))
end
Base.invokelatest(g, x...)
end
_invoke (generic function with 1 method)
julia> _invoke(f, 1, 2; generated=true)
1
julia> _invoke(f, 1, 2; generated=false)
2
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I asked this on stack overflow a while back.
Did not get a great answer
https://stackoverflow.com/questions/58612962/how-do-i-test-both-sides-of-a-if-generated
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This answer seems a bit cleaner to me
Just found this: https://github.com/JuliaData/Tables.jl/issues/144#issue-562125911. Haven’t looked into the details though.