test: add test for extend with parameter dependencies

test/parameter_dependencies.jl

@@ -49,6 +49,24 @@ using NonlinearSolve
     @test integ.ps[p2] == 10.0
 end
 
+@testset "extend" begin
+    @parameters p1=1.0 p2=1.0
+    @variables x(t)
+
+    @mtkbuild sys1 = ODESystem(
+        [D(x) ~ p1 * t + p2],
+        t
+    )
+    @named sys2 = ODESystem(
+        [],
+        t;
+        parameter_dependencies = [p2 => 2p1]
+    )
+    sys = extend(sys2, sys1)
+    @test isequal(only(parameters(sys)), p1)
+    @test Set(full_parameters(sys)) == Set([p1, p2])
+end
+
 @testset "Clock system" begin
     dt = 0.1
     @variables x(t) y(t) u(t) yd(t) ud(t) r(t) z(t)