Add test

Author: YingboMa

test/odesystem.jl

@@ -746,3 +746,12 @@ let
     @named sys = ODESystem(eqs, t, vars, pars)
     @test_throws ModelingToolkit.ExtraEquationsSystemException structural_simplify(sys)
 end
+
+# 1561
+let
+    vars = @variables x y
+    arr = ModelingToolkit.varmap_to_vars([x => 0.0, y => [0.0, 1.0]], vars) #error
+    sol = Union{Float64, Vector{Float64}}[0.0, [0.0, 1.0]]
+    @test arr == sol
+    @test typeof(arr) == typeof(sol)
+end