Fix downstream test

NT.get_unit assumes DynamicQuantities, to use Unitful use
MT.UnitfulUnitCheck.get_unit.

test/downstream/modeling_toolkit_utils.jl

@@ -1,34 +1,58 @@
 using Symbolics: diff2term
 using ModelingToolkit
-using ModelingToolkit: equivalent, get_unit, value, VariableUnit
-using Unitful: @u_str
+using ModelingToolkit: equivalent, get_unit, value, VariableUnit, UnitfulUnitCheck
+using DynamicQuantities: @u_str as @du_str
+using Unitful: @u_str as @uu_str
 using Test
 
-@variables t [unit = u"s"] k(t)
+@variables t [unit = du"s"] k(t)
 D = Differential(t)
 
 @test equivalent(
-    u"1/s",
+    du"s^-1",
     get_unit(
         diff2term(
-            value(D(k)),
-            Dict(VariableUnit => get_unit(D(k)))
-        )
+        value(D(k)),
+        Dict(VariableUnit => get_unit(D(k)))
+    )
     )
 )
 
 @test equivalent(
-    u"1/s^2",
+    du"s^-2",
     get_unit(
         diff2term(
-            value(D(D(k))),
-            Dict(VariableUnit => get_unit(D(D(k))))
-        )
+        value(D(D(k))),
+        Dict(VariableUnit => get_unit(D(D(k))))
+    )
+    )
+)
+
+@variables t [unit = uu"s"] k(t)
+D = Differential(t)
+
+@test equivalent(
+    uu"s^-1",
+    UnitfulUnitCheck.get_unit(
+        diff2term(
+        value(D(k)),
+        Dict(VariableUnit => UnitfulUnitCheck.get_unit(D(k)))
+    )
+    )
+)
+
+@test equivalent(
+    uu"s^-2",
+    UnitfulUnitCheck.get_unit(
+        diff2term(
+        value(D(D(k))),
+        Dict(VariableUnit => UnitfulUnitCheck.get_unit(D(D(k))))
+    )
     )
 )
 
 @variables x y t
 D = Differential(t)
 Symbolics.diff2term(D(x))
-Symbolics.diff2term(D(sqrt(sqrt(sqrt(+(x,y))))))
-Symbolics.diff2term(D(x+y))
+Symbolics.diff2term(D(sqrt(sqrt(sqrt(+(x, y))))))
+Symbolics.diff2term(D(x + y))