Fix tests for ZygoteRule change

Project.toml

@@ -46,7 +46,7 @@ Requires = "1.1"
 PrecompileTools = "1"
 SpecialFunctions = "1.6, 2"
 Tracker = "0.2"
-ZygoteRules = "0.2.1"
+ZygoteRules = "0.2.4"
 julia = "1.6"
 
 [extensions]

test/gradcheck.jl

@@ -114,7 +114,7 @@ end
  @test gradtest(X -> sum(sum(x -> x^2, X; dims=1)), randn(10)) # issue #681
 
  # Non-differentiable sum of booleans
- @test gradient(sum, [true, false, true]) == (nothing,)
+ @test gradient(sum, [true, false, true]) === nothing
  @test gradient(x->sum(x .== 0.0), [1.2, 0.2, 0.0, -1.1, 100.0]) == (nothing,)
 
  # https://github.com/FluxML/Zygote.jl/issues/314
@@ -178,7 +178,7 @@ end
 
  # Ensure that nothings work with non-numeric types.
  _, back = Zygote.pullback(getindex, [randn(2) for _ in 1:3], [1])
- @test back([nothing]) == (nothing, nothing)
+ @test back([nothing]) === nothing
 end
 
 @testset "view" begin

test/structures.jl

@@ -64,5 +64,5 @@ end
  end
 
  m, b = Zygote._pullback(Zygote.Context(), nameof, M)
- @test b(m) == (nothing, nothing)
+ @test b(m) === nothing
 end