Better document test_rrule tweak (#113)

test/systematic.jl

@@ -46,22 +46,22 @@ function make_implicit_sqrt(; kwargs...)
 end
 
 function make_implicit_sqrt_byproduct(; kwargs...)
-    forward(x) = mysqrt(x), eltype(x)(2)  # fails rrule tests with 2 integer, probably due to https://juliadiff.org/ChainRulesTestUtils.jl/dev/index.html#Specifying-Tangents
-    conditions(x, y, z::Number) = y .^ z .- abs.(change_shape(x))
+    forward(x) = mysqrt(x), 2
+    conditions(x, y, z::Integer) = y .^ z .- abs.(change_shape(x))
     implicit = ImplicitFunction(forward, conditions; kwargs...)
     return implicit
 end
 
 function make_implicit_power_args(; kwargs...)
-    forward(x, p::Number) = mypower(x, one(eltype(x)) / p)
-    conditions(x, y, p::Number) = y .^ p .- abs.(change_shape(x))
+    forward(x, p::Integer) = mypower(x, one(eltype(x)) / p)
+    conditions(x, y, p::Integer) = y .^ p .- abs.(change_shape(x))
     implicit = ImplicitFunction(forward, conditions; kwargs...)
     return implicit
 end
 
 function make_implicit_power_kwargs(; kwargs...)
-    forward(x; p::Number) = mypower(x, one(eltype(x)) / p)
-    conditions(x, y; p::Number) = y .^ p .- abs.(change_shape(x))
+    forward(x; p::Integer) = mypower(x, one(eltype(x)) / p)
+    conditions(x, y; p::Integer) = y .^ p .- abs.(change_shape(x))
     implicit = ImplicitFunction(forward, conditions; kwargs...)
     return implicit
 end
@@ -243,7 +243,7 @@ function test_implicit_rrule(rc, x::AbstractArray{T}; kwargs...) where {T}
 
     @testset "ChainRulesTestUtils" begin
         test_rrule(rc, imf1, x; atol=1e-2)
-        test_rrule(rc, imf2, x; atol=5e-2)
+        test_rrule(rc, imf2, x; atol=5e-2, output_tangent=(dy, 0)) # see issue https://github.com/gdalle/ImplicitDifferentiation.jl/issues/112
         test_rrule(rc, imf3, x, 2; atol=1e-2)
         test_rrule(rc, imf4, x; atol=1e-2, fkwargs=(p=2,))
     end