test: use symbolic save_idxs in tests

Author: AayushSabharwal

test/downstream/solution_interface.jl

@@ -191,21 +191,13 @@ end
             ss1.state_map == ss2.state_map
         end
 
-        ode_sol = solve(prob, Tsit5(); save_idxs = xidx)
-        subsys = SciMLBase.SavedSubsystem(sys, prob.p, [xidx])
-        @test SciMLBase.get_saved_state_idxs(subsys) == [xidx]
-
-        # FIXME: hack for save_idxs
-        SciMLBase.@reset ode_sol.saved_subsystem = subsys
+        ode_sol = solve(prob, Tsit5(); save_idxs = [x])
 
         @mtkbuild sys = ODESystem([D(x) ~ x + p * y, 1 ~ sin(y) + cos(x)], t)
         xidx = variable_index(sys, x)
         prob = DAEProblem(sys, [D(x) => x + p * y, D(y) => 1 / sqrt(1 - (1 - cos(x))^2)],
-            [x => 1.0, y => asin(1 - cos(x))], (0.0, 1.0), [p => 2.0])
-        dae_sol = solve(prob, DFBDF(); save_idxs = xidx)
-        subsys = SciMLBase.SavedSubsystem(sys, prob.p, [xidx])
-        # FIXME: hack for save_idxs
-        SciMLBase.@reset dae_sol.saved_subsystem = subsys
+            [x => 1.0, y => asin(1 - cos(x))], (0.0, 1.0), [p => 2.0]; build_initializeprob = false)
+        dae_sol = solve(prob, DFBDF(); save_idxs = [x])
 
         @brownian a b
         @mtkbuild sys = System([D(x) ~ x + p * y + x * a, D(y) ~ 2p + x^2 + y * b], t)
@@ -256,21 +248,11 @@ end
 
         @test SciMLBase.SavedSubsystem(sys, prob.p, [x, y, q, r, s, u]) === nothing
 
-        sol = solve(prob; save_idxs = xidx)
+        sol = solve(prob; save_idxs = [x, q, r])
         xvals = sol[x]
-        subsys = SciMLBase.SavedSubsystem(sys, prob.p, [x, q, r])
-        @test SciMLBase.get_saved_state_idxs(subsys) == [xidx]
+        @test SciMLBase.get_saved_state_idxs(sol.saved_subsystem) == [xidx]
         qvals = sol.ps[q]
         rvals = sol.ps[r]
-        # FIXME: hack for save_idxs
-        SciMLBase.@reset sol.saved_subsystem = subsys
-        discq = DiffEqArray(SciMLBase.TupleOfArraysWrapper.(tuple.(Base.vect.(qvals))),
-            sol.discretes[qpidx.timeseries_idx].t, (1, 1))
-        discr = DiffEqArray(SciMLBase.TupleOfArraysWrapper.(tuple.(Base.vect.(rvals))),
-            sol.discretes[rpidx.timeseries_idx].t, (1, 1))
-        SciMLBase.@reset sol.discretes.collection[qpidx.timeseries_idx] = discq
-        SciMLBase.@reset sol.discretes.collection[rpidx.timeseries_idx] = discr
-
         @test sol[x] == xvals
 
         @test all(Base.Fix1(is_parameter, sol), [p, q, r, s, u])