test: improve analysis point test

Author: AayushSabharwal

test/downstream/analysis_points.jl

@@ -485,5 +485,10 @@ end
         systems = [model, inverse_model, pid, filt, sensor, inverse_sensor, r, add],
         name = :closed_loop)
     # just ensure the system simplifies
-    Blocks.get_sensitivity(closed_loop, :y)
+    mats, _ = get_sensitivity(closed_loop, :y)
+    S = CS.ss(mats...)
+    fr = CS.freqrespv(S, [0.01, 1, 100])
+    # https://github.com/SciML/ModelingToolkit.jl/pull/3469
+    reference_fr = ComplexF64[-1.2505330104772838e-11 - 2.500062613816021e-9im, -0.0024688370221621625 - 0.002279011866413123im, 1.8100018764334602 + 0.3623845793211718im]
+    @test isapprox(fr, reference_fr)
 end