test: add test for defaults fix

Author: AayushSabharwal

test/extensions/Project.toml

@@ -1,5 +1,6 @@
 [deps]
 BifurcationKit = "0f109fa4-8a5d-4b75-95aa-f515264e7665"
+ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 ModelingToolkit = "961ee093-0014-501f-94e3-6117800e7a78"
 OrdinaryDiffEq = "1dea7af3-3e70-54e6-95c3-0bf5283fa5ed"
 SciMLSensitivity = "1ed8b502-d754-442c-8d5d-10ac956f44a1"

test/extensions/ad.jl

@@ -5,6 +5,7 @@ using SymbolicIndexingInterface
 using SciMLStructures
 using OrdinaryDiffEq
 using SciMLSensitivity
+using ForwardDiff
 
 @variables x(t)[1:3] y(t)
 @parameters p[1:3, 1:3] q
@@ -27,3 +28,26 @@ gs = gradient(new_p) do new_p
     new_sol = solve(new_prob, Tsit5())
     sum(new_sol)
 end
+
+@testset "Issue#2997" begin
+    pars = @parameters y0 mh Tγ0 Th0 h ργ0
+    vars = @variables x(t)
+    @named sys = ODESystem([D(x) ~ y0],
+        t,
+        vars,
+        pars;
+        defaults = [
+            y0 => mh * 3.1 / (2.3 * Th0),
+            mh => 123.4,
+            Th0 => (4 / 11)^(1 / 3) * Tγ0,
+            Tγ0 => (15 / π^2 * ργ0 * (2 * h)^2 / 7)^(1 / 4) / 5
+        ])
+    sys = structural_simplify(sys)
+
+    function x_at_0(θ)
+        prob = ODEProblem(sys, [sys.x => 1.0], (0.0, 1.0), [sys.ργ0 => θ[1], sys.h => θ[2]])
+        return prob.u0[1]
+    end
+
+    @test ForwardDiff.gradient(x_at_0, [0.3, 0.7]) == zeros(2)
+end