add tests, frule is broken

Author: mcabbott

test/runtests.jl

@@ -1,8 +1,8 @@
 using Diffractor
-using Diffractor: var"'", ∂⃖
+using Diffractor: var"'", ∂⃖, DiffractorRuleConfig
 using ChainRules
 using ChainRulesCore
-using ChainRules: ZeroTangent, NoTangent
+using ChainRules: ZeroTangent, NoTangent, frule_via_ad, rrule_via_ad
 using Symbolics
 
 using Test
@@ -195,4 +195,13 @@ end
 # Issue #40 - Symbol type parameters not properly quoted
 @test Diffractor.∂⃖recurse{1}()(Val{:transformations})[1] === Val{:transformations}()
 
+# PR # 45 - Calling back into AD from ChainRules
+y45, back45 = rrule_via_ad(DiffractorRuleConfig(), x -> log(exp(x)), 2.0)
+@test y45 ≈ 2.0
+@test back45(1) == (ZeroTangent(), 1.0)
+
+# z45, delta45 = frule_via_ad(DiffractorRuleConfig(), (0,1), x -> log(exp(x)), 2.0)
+# @test z45 ≈ 2.0
+# @test delta45 ≈ 1.0
+
 include("pinn.jl")