Update ad_utils.jl

Author: yebai

test/test_utils/ad_utils.jl

@@ -22,14 +22,6 @@ adbackends = [
     Turing.AutoForwardDiff(; chunksize=0), Turing.AutoReverseDiff(; compile=false)
 ]
 
-# Tapir isn't supported for older Julia versions, hence the check.
-install_tapir = isdefined(Turing, :AutoTapir)
-if install_tapir
-    # TODO(mhauru) Is there a better way to install optional dependencies like this?
-    Pkg.add("Tapir")
-    push!(adbackends, Turing.AutoTapir(false))
-end
-
 # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
 # Stuff for checking that the right AD backend is being used.
 
@@ -62,6 +54,15 @@ const eltypes_by_adtype = Dict(
     ),
 )
 
+# Tapir isn't supported for older Julia versions, hence the check.
+install_tapir = isdefined(Turing, :AutoTapir)
+if install_tapir
+    # TODO(mhauru) Is there a better way to install optional dependencies like this?
+    Pkg.add("Tapir")
+    push!(adbackends, Turing.AutoTapir(false))
+    push!(eltypes_by_adtype, Turing.AutoTapir => (Tapir.CoDual,))
+end
+
 """
     AbstractWrongADBackendError