diff --git a/.github/workflows/generate.yml b/.github/workflows/generate.yml
index fd8347c..e1b6530 100644
--- a/.github/workflows/generate.yml
+++ b/.github/workflows/generate.yml
@@ -17,9 +17,9 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Python 3.x
-      uses: actions/setup-python@v4
+      uses: actions/setup-python@v5
       with:
         # Semantic version range syntax or exact version of a Python version
         python-version: '3.x'
@@ -44,11 +44,11 @@ jobs:
     runs-on: ubuntu-latest
     needs: build
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Install iverilog
       run: sudo apt install iverilog
     - name: Set up Python 3.x
-      uses: actions/setup-python@v4
+      uses: actions/setup-python@v5
       with:
         # Semantic version range syntax or exact version of a Python version
         python-version: '3.x'
@@ -90,9 +90,9 @@ jobs:
         python-version: [ '3.7', '3.8', '3.9', '3.10', '3.11' ]
     name: Python ${{ matrix.python-version }} test
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Setup python
-      uses: actions/setup-python@v4
+      uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
         architecture: x64
@@ -107,9 +107,9 @@ jobs:
     needs: test
     if: github.ref == 'refs/heads/main'
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Python 3.x
-      uses: actions/setup-python@v4
+      uses: actions/setup-python@v5
       with:
         # Semantic version range syntax or exact version of a Python version
         python-version: '3.x'
@@ -123,7 +123,7 @@ jobs:
     - name: Generate documentation
       run: pdoc --html ariths_gen
     - name: Upload results
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: documentation
         path: html
diff --git a/ariths_gen/multi_bit_circuits/others/popcount.py b/ariths_gen/multi_bit_circuits/others/popcount.py
index 04fcda3..4721bce 100644
--- a/ariths_gen/multi_bit_circuits/others/popcount.py
+++ b/ariths_gen/multi_bit_circuits/others/popcount.py
@@ -1,7 +1,7 @@
 """
 
 """
-from typing import Union
+from typing import Union, Optional
 
 from ariths_gen.wire_components import (
     Wire,
@@ -45,7 +45,7 @@ class UnsignedPopCount(GeneralCircuit):
 
     """
 
-    def __init__(self, a: Bus, adder : Union[ArithmeticCircuit, None] = None, prefix : str = "", name : str = "popcnt", **kwargs):
+    def __init__(self, a: Bus, adder : Optional[ArithmeticCircuit] = None, prefix : str = "", name : str = "popcnt", **kwargs):
         self.N = a.N
         self.a = a
 
diff --git a/tests/test_all.py b/tests/test_all.py
index bcd9342..5a22005 100644
--- a/tests/test_all.py
+++ b/tests/test_all.py
@@ -381,6 +381,25 @@ def test_wire_as_bus():
     assert r.sum() == 1
     assert r[-1, -1, -1] == 1
 
+def test_unique():
+    from ariths_gen.wire_components import Wire, Bus
+    import pytest
+    import sys
+    from ariths_gen.one_bit_circuits.logic_gates import AndGate
+    from ariths_gen.one_bit_circuits.one_bit_components import TwoOneMultiplexer
+    from ariths_gen.core.arithmetic_circuits import GeneralCircuit
+
+    class test_circuit(GeneralCircuit):
+        def __init__(self, a: Bus, prefix="test_circuit", **kwargs):
+            super().__init__(prefix=prefix, name="test_circuit", inputs=[a], out_N=1, **kwargs)
+            g = self.add_component(AndGate(a[0], a[1], prefix="g2"))
+            g2 = self.add_component(AndGate(g.out, a[2], prefix="g2"))
+            g3 = self.add_component(AndGate(g2.out, g.out, prefix="g2"))
+            self.out[0] = g3.out
+
+    with pytest.raises(AssertionError):
+        circ = test_circuit(Bus("a", 3), "c1")
+        circ.get_v_code_flat(file_object=sys.stdout)
 
 if __name__ == "__main__":
     test_unsigned_approxmul()
diff --git a/tests/test_popcnt.py b/tests/test_popcnt.py
index 52de63f..a877254 100644
--- a/tests/test_popcnt.py
+++ b/tests/test_popcnt.py
@@ -1,3 +1,4 @@
+from io import StringIO
 from ariths_gen.core.cgp_circuit import UnsignedCGPCircuit
 from ariths_gen.wire_components import (
     Wire,
@@ -11,6 +12,7 @@ from ariths_gen.core.arithmetic_circuits import GeneralCircuit
 from ariths_gen.multi_bit_circuits.others import (
     UnsignedPopCount
 )
+import numpy as np
 
 
 def test_popcount():