Test symbolic array state codegen

Add a focused regression that compiles a StateSpace block with array states and constructs its ODEProblem under downgraded dependencies.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>

Author: ChrisRackauckas

test/array_state_codegen.jl

@@ -0,0 +1,22 @@
+using ModelingToolkitBase: System, connect, mtkcompile, @named, t_nounits
+using ModelingToolkitStandardLibrary.Blocks: Constant, StateSpace
+using SciMLBase: ODEProblem
+using Test
+
+@testset "Array state codegen" begin
+    A = [0 1; -1 -0.5]
+    B = [0, 1]
+    C = [0.9 1;]
+    D = [0;;]
+    @named ss = StateSpace(; A, B, C, D, x = zeros(2))
+    @named source = Constant(; k = 1)
+    @named model = System(
+        connect(source.output, ss.input),
+        t_nounits,
+        systems = [ss, source]
+    )
+
+    sys = mtkcompile(model)
+    prob = ODEProblem(sys, Pair[], (0.0, 1.0))
+    @test prob.u0 == zeros(2)
+end