diff --git a/src/SpaceExParser.jl b/src/SpaceExParser.jl
index 719fca5..8335a3f 100644
--- a/src/SpaceExParser.jl
+++ b/src/SpaceExParser.jl
@@ -6,11 +6,17 @@ export readsxmodel, writesxmodel
 Load dependencies
 =========================================#
 
-using HybridSystems, LazySets
 using DataStructures: OrderedDict
-import MathematicalSystems
-using MathematicalSystems: AbstractSystem, AbstractContinuousSystem,
-                           LinearContinuousSystem, LinearControlContinuousSystem,
+using EzXML: readxml, root, eachelement, nodename, nodecontent
+using HybridSystems: AbstractSwitching, AutonomousSwitching, GraphAutomaton,
+                     HybridSystem, add_transition!, assignment, guard, inputdim,
+                     inputset, nmodes, ntransitions, resetmap, source, statedim,
+                     stateset, target, transitions
+using LazySets: LazySets, AbstractHyperrectangle, HalfSpace, Hyperplane,
+                Intersection, LazySet, Singleton, dim, high, isuniversal, low
+using MathematicalSystems: MathematicalSystems, AbstractSystem,
+                           AbstractContinuousSystem, LinearContinuousSystem,
+                           LinearControlContinuousSystem,
                            AffineContinuousSystem,
                            AffineControlContinuousSystem,
                            ConstrainedLinearContinuousSystem,
@@ -18,8 +24,7 @@ using MathematicalSystems: AbstractSystem, AbstractContinuousSystem,
                            ConstrainedLinearControlDiscreteSystem,
                            ConstrainedAffineContinuousSystem,
                            ConstrainedAffineControlContinuousSystem
-using EzXML: readxml, root, eachelement, nodename, nodecontent
-using SymEngine: Basic, subs
+using SymEngine: Basic, free_symbols, subs
 
 import Base: convert
 
diff --git a/src/parse.jl b/src/parse.jl
index da66337..3505eef 100644
--- a/src/parse.jl
+++ b/src/parse.jl
@@ -1,4 +1,4 @@
-const _parse_s = Base.Meta.parse
+const _parse_s = Base.Meta.parse  # NOTE: this is an internal function
 const _parse_t = Base.parse
 
 """
diff --git a/src/symbolic.jl b/src/symbolic.jl
index 98c1c2c..9d6e3fe 100644
--- a/src/symbolic.jl
+++ b/src/symbolic.jl
@@ -208,16 +208,16 @@ end
 # ref_tuple is used for the error message
 function _add_invariants!(X, U, invariants, state_variables, input_variables, ref_tuple)
     for invi in invariants
-        if LazySets._ishyperplanar(invi)
+        if LazySets._ishyperplanar(invi)  # NOTE: this is an internal function
             set_type = Hyperplane{NUM}
-        elseif LazySets._ishalfspace(invi)
+        elseif LazySets._ishalfspace(invi)  # NOTE: this is an internal function
             set_type = HalfSpace{NUM}
         else
             loc_or_trans, id = ref_tuple
             error_msg_set(loc_or_trans, invi, id)
         end
 
-        vars = LazySets.free_symbols(invi, set_type)
+        vars = free_symbols(invi, set_type)
         got_state_invariant = all(si in state_variables for si in vars)
         got_input_invariant = all(si in input_variables for si in vars)
         if got_state_invariant
diff --git a/test/Aqua.jl b/test/Aqua.jl
deleted file mode 100644
index 2d9d73d..0000000
--- a/test/Aqua.jl
+++ /dev/null
@@ -1,6 +0,0 @@
-using SpaceExParser, Test
-import Aqua
-
-@testset "Aqua tests" begin
-    Aqua.test_all(SpaceExParser)
-end
diff --git a/test/Project.toml b/test/Project.toml
index 7148428..99ae738 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -1,5 +1,6 @@
 [deps]
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
+ExplicitImports = "7d51a73a-1435-4ff3-83d9-f097790105c7"
 EzXML = "8f5d6c58-4d21-5cfd-889c-e3ad7ee6a615"
 HybridSystems = "2207ec0c-686c-5054-b4d2-543502888820"
 LazySets = "b4f0291d-fe17-52bc-9479-3d1a343d9043"
@@ -8,6 +9,7 @@ Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [compat]
 Aqua = "0.8.9"
+ExplicitImports = "1"
 EzXML = "1"
 HybridSystems = "0.4"
 LazySets = "3, 4, 5"
diff --git a/test/quality_assurance.jl b/test/quality_assurance.jl
new file mode 100644
index 0000000..86e0f65
--- /dev/null
+++ b/test/quality_assurance.jl
@@ -0,0 +1,18 @@
+using SpaceExParser, Test
+import Aqua, ExplicitImports
+
+@testset "ExplicitImports tests" begin
+    @test isnothing(ExplicitImports.check_all_explicit_imports_are_public(SpaceExParser))
+    @test isnothing(ExplicitImports.check_all_explicit_imports_via_owners(SpaceExParser))
+    ignores = (:_ishalfspace, :_ishyperplanar, :parse,)
+    @test isnothing(ExplicitImports.check_all_qualified_accesses_are_public(SpaceExParser;
+                                                                            ignore=ignores))
+    @test isnothing(ExplicitImports.check_all_qualified_accesses_via_owners(SpaceExParser))
+    @test isnothing(ExplicitImports.check_no_implicit_imports(SpaceExParser))
+    @test isnothing(ExplicitImports.check_no_self_qualified_accesses(SpaceExParser))
+    @test isnothing(ExplicitImports.check_no_stale_explicit_imports(SpaceExParser))
+end
+
+@testset "Aqua tests" begin
+    Aqua.test_all(SpaceExParser)
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 05fb946..72309ea 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -7,4 +7,4 @@ include("unit_parse.jl")
     include("unit_affine.jl")
 end
 
-include("Aqua.jl")
+include("quality_assurance.jl")