Fix some odd test choices

Author: ChrisRackauckas

src/systems/nonlinear/initializesystem.jl

@@ -33,7 +33,7 @@ function generate_initializesystem(sys::ODESystem;
         if u0map === nothing || isempty(u0map)
             filtered_u0 = u0map
         else
-            filtered_u0 = []
+            filtered_u0 = Pair[]
             for x in u0map
                 y = get(schedule.dummy_sub, x[1], x[1])
                 y = get(diffmap, y, y)
@@ -51,10 +51,9 @@ function generate_initializesystem(sys::ODESystem;
                 elseif y ∈ set_full_states
                     push!(filtered_u0, y => x[2])
                 else
-                    error("Unreachable. Open an issue")
+                    error("Initialization expression $y is currently not supported. If its a higher order derivative expression, then only the dummy derivative expressions are supported.")
                 end
             end
-            filtered_u0 = reduce(vcat, filtered_u0)
             filtered_u0 = filtered_u0 isa Pair ? todict([filtered_u0]) : todict(filtered_u0)
         end
     else

test/odesystem.jl

@@ -671,7 +671,8 @@ let
     @test isapprox(sol[x[1]][end], 2, atol = 1e-3)
 
     # no initial conditions for D(x[1]) and D(x[2]) provided
-    @test_throws ArgumentError prob=DAEProblem(sys, Pair[], Pair[], (0, 50))
+    @test_throws ModelingToolkit.MissingVariablesError prob=DAEProblem(
+        sys, Pair[], Pair[], (0, 50))
 
     prob = ODEProblem(sys, Pair[x[1] => 0], (0, 50))
     sol = solve(prob, Rosenbrock23())

test/structural_transformation/index_reduction.jl

@@ -138,10 +138,6 @@ let sys = structural_simplify(pendulum2)
     @test length(unknowns(sys)) == 5
 
     u0 = [
-        D(x) => 0.0,
-        D(D(x)) => 0.0,
-        D(y) => 0.0,
-        D(D(y)) => 0.0,
         x => sqrt(2) / 2,
         y => sqrt(2) / 2
     ]