test: update error checking tests for improved error in better_varmap_to_vars

Author: AayushSabharwal

test/implicit_discrete_system.jl

@@ -28,7 +28,7 @@ rng = StableRNG(22525)
     @test prob.u0 == [1.0, 1.0]
     @variables x(t)
     @mtkbuild sys = System([x(k) ~ x(k) * x(k - 1) - 3], t)
-    @test_throws ModelingToolkit.MissingVariablesError prob=ImplicitDiscreteProblem(
+    @test_throws ModelingToolkit.MissingGuessError prob=ImplicitDiscreteProblem(
         sys, [], tspan)
 end
 

test/initializationsystem.jl

@@ -495,7 +495,7 @@ sys = extend(sysx, sysy)
     @variables x(t) y(t)
     @named sys = System([x^2 + y^2 ~ 25, D(x) ~ 1], t)
     ssys = structural_simplify(sys)
-    @test_throws ModelingToolkit.MissingVariablesError ODEProblem(
+    @test_throws ModelingToolkit.MissingGuessError ODEProblem(
         ssys, [x => 3], (0, 1)) # y should have a guess
 end