fixup! refactor: don't splat MTKParameters into observed functions anymore

Author: AayushSabharwal

test/input_output_handling.jl

@@ -144,9 +144,9 @@ if VERSION >= v"1.8" # :opaque_closure not supported before
             drop_expr = identity)
         x = randn(size(A, 1))
         u = randn(size(B, 2))
-        p = getindex.(
+        p = (getindex.(
             Ref(ModelingToolkit.defaults_and_guesses(ssys)),
-            parameters(ssys))
+            parameters(ssys)),)
         y1 = obsf(x, u, p, 0)
         y2 = C * x + D * u
         @test y1[] ≈ y2[]

test/reduction.jl

@@ -119,7 +119,7 @@ prob1 = ODEProblem(reduced_system, u0, (0.0, 100.0), pp)
 solve(prob1, Rodas5())
 
 prob2 = SteadyStateProblem(reduced_system, u0, pp)
-@test prob2.f.observed(lorenz2.u, prob2.u0, pp) === 1.0
+@test prob2.f.observed(lorenz2.u, prob2.u0, prob2.p) === 1.0
 
 # issue #724 and #716
 let