fix some AD tests

Author: lkdvos

test/ad.jl

@@ -1,6 +1,6 @@
 using ChainRulesCore
 using ChainRulesTestUtils
-using FiniteDifferences: FiniteDifferences
+using FiniteDifferences: FiniteDifferences, central_fdm, forward_fdm
 using Random
 using LinearAlgebra
 using Zygote
@@ -305,9 +305,11 @@ for V in spacelist
                 (T <: Real && f === sqrt) ? randexp!(d.data) : randn!(d.data)
                 d2 = DiagonalTensorMap{T}(undef, V[1])
                 (T <: Real && f === sqrt) ? randexp!(d2.data) : randn!(d2.data)
-                test_rrule(f, t1; rrule_f=Zygote.rrule_via_ad, check_inferred)
-                test_rrule(f, t2; rrule_f=Zygote.rrule_via_ad, check_inferred)
-                test_rrule(f, d; check_inferred, output_tangent=d2)
+
+                fdm = (T <: Real && f === sqrt) ? forward_fdm(5, 1) : central_fdm(5, 1)
+                test_rrule(f, t1; rrule_f=Zygote.rrule_via_ad, check_inferred, fdm)
+                test_rrule(f, t2; rrule_f=Zygote.rrule_via_ad, check_inferred, fdm)
+                test_rrule(f, d; check_inferred, output_tangent=d2, fdm)
             end
         end
 
@@ -516,7 +518,7 @@ for V in spacelist
                     test_ad_rrule(last ∘ eig_full, t; output_tangent=Δv, atol, rtol)
                     test_ad_rrule(eig_full, t; output_tangent=(Δd2, Δv), atol, rtol)
 
-                    add!(t, t')
+                    t += t'
                     d, v = eigh_full(t)
                     Δv = rand_tangent(v)
                     Δd = rand_tangent(d)