=fix mistake in non-tuple output message

Author: oxinabox

Project.toml

@@ -1,6 +1,6 @@
 name = "ChainRulesTestUtils"
 uuid = "cdddcdb0-9152-4a09-a978-84456f9df70a"
-version = "0.7.11"
+version = "0.7.12"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/testers.jl

@@ -244,9 +244,14 @@ function test_rrule(
 
         check_inferred && _test_inferred(pullback, ȳ)
         ad_cotangents = pullback(ȳ)
-        ad_cotangents isa Tuple || error("The pullback must return (∂self, ∂args...), not $∂s.")
-        msg = "The pullback should return 1 cotangent for the primal and each primal input."
-        @test_msg msg length(ad_cotangents) == 1 + length(args)
+        @test_msg(
+            "The pullback must return a Tuple (∂self, ∂args...)",
+            ad_cotangents isa Tuple
+        )
+        @test_msg(
+            "The pullback should return 1 cotangent for the primal and each primal input.",
+            (ad_cotangents) == 1 + length(args)
+        )
 
         # Correctness testing via finite differencing.
         # TODO: remove Nothing when https://github.com/JuliaDiff/ChainRulesTestUtils.jl/issues/113

test/testers.jl

@@ -548,6 +548,15 @@ struct MySpecialConfig <: RuleConfig{Union{MySpecialTrait}} end
             @test fails(() -> test_frule(foo, 2.1, 2.1))
             @test fails(() -> test_rrule(foo, 21.0, 32.0))
         end
+
+        @testset "rrule not returning a tuple" begin
+            bar(x, y) = x + 3y
+            function ChainRulesCore.rrule(::typeof(bar), x, y)
+                bar_pullback(dy) = dy
+                return bar(x,y), bar_pullback
+            end
+            @test fails(() -> test_rrule(bar, 21.0, 32.0))
+        end
     end
 
     @testset "structs" begin