fix possible test failure

Author: ChrisRackauckas

test/downstream/default_linsolve_structure.jl

@@ -5,24 +5,37 @@ jac = (J,u,p,t) -> (J[1,1] = 1/t; J[2,2] = 1/t; J)
 jp_diag = Diagonal(zeros(2))
 fun = ODEFunction(f; jac=jac, jac_prototype=jp_diag)
 prob = ODEProblem(fun,ones(2),(1.0,10.0))
+sol = solve(prob,Rosenbrock23())
+@test sol[end] ≈ [10.0,10.0]
+@test length(sol) < 60
+
 sol = solve(prob,Rosenbrock23(autodiff=false))
 @test sol[end] ≈ [10.0,10.0]
 @test length(sol) < 60
 
 jp = Tridiagonal(jp_diag)
 fun = ODEFunction(f; jac=jac, jac_prototype=jp)
 prob = ODEProblem(fun,ones(2),(1.0,10.0))
+
+sol = solve(prob,Rosenbrock23())
+@test sol[end] ≈ [10.0,10.0]
+@test length(sol) < 60
+
 sol = solve(prob,Rosenbrock23(autodiff=false))
 @test sol[end] ≈ [10.0,10.0]
 @test length(sol) < 60
 
 jp = SymTridiagonal(jp_diag)
 fun = ODEFunction(f; jac=jac, jac_prototype=jp)
 prob = ODEProblem(fun,ones(2),(1.0,10.0))
-sol = solve(prob,Rosenbrock23(autodiff=false))
+sol = solve(prob,Rosenbrock23())
 @test sol[end] ≈ [10.0,10.0]
 @test length(sol) < 60
 
+# Don't test the autodiff=false version here because it's not as numerically stable,
+# so lack of optimizations would lead to unsymmetric which causes an error:
+# LoadError: ArgumentError: broadcasted assignment breaks symmetry between locations (1, 2) and (2, 1)
+
 @test_broken begin
     jp = Hermitian(jp_diag)
     fun = ODEFunction(f; jac=jac, jac_prototype=jp)