diff --git a/tests/test_all_test_functions.py b/tests/test_all_test_functions.py
index ca70bf0..d079b10 100644
--- a/tests/test_all_test_functions.py
+++ b/tests/test_all_test_functions.py
@@ -25,7 +25,7 @@ def test_all_mathematical_functions(test_function):
 
     hyper = Hyperactive()
     hyper.add_search(
-        test_function_,
+        test_function_.objective_function,
         test_function_.create_n_dim_search_space(value_types="list"),
         n_iter=15,
     )
@@ -38,7 +38,7 @@ def test_all_machine_learning_functions(test_function):
 
     hyper = Hyperactive()
     hyper.add_search(
-        test_function_,
+        test_function_.objective_function,
         test_function_.search_space,
         n_iter=15,
     )
diff --git a/tests/test_arrays_input.py b/tests/test_arrays_input.py
index ca46743..62ec524 100644
--- a/tests/test_arrays_input.py
+++ b/tests/test_arrays_input.py
@@ -34,8 +34,8 @@
 styblinski_tang_function = StyblinskiTangFunction(2, input_type="arrays")
 
 
-objective_function_para_2D = (
-    "objective_function",
+test_function_para_2D = (
+    "test_function",
     [
         (sphere_function),
         (rastrigin_function),
@@ -57,6 +57,6 @@
 b = np.array([1, 2, 3, 4, 5])
 
 
-@pytest.mark.parametrize(*objective_function_para_2D)
-def test_array_input(objective_function):
-    objective_function(a, b)
+@pytest.mark.parametrize(*test_function_para_2D)
+def test_array_input(test_function):
+    test_function.objective_function(a, b)
diff --git a/tests/test_optimization.py b/tests/test_optimization.py
index 57938c1..9fa94e6 100644
--- a/tests/test_optimization.py
+++ b/tests/test_optimization.py
@@ -36,7 +36,7 @@
 
 
 objective_function_para_2D = (
-    "objective_function",
+    "test_function",
     [
         (sphere_function),
         (rastrigin_function),
@@ -57,14 +57,14 @@
 
 
 @pytest.mark.parametrize(*objective_function_para_2D)
-def test_optimization_2D(objective_function):
+def test_optimization_2D(test_function):
     search_space = {
         "x0": np.arange(0, 100, 1),
         "x1": np.arange(0, 100, 1),
     }
 
     opt = RandomSearchOptimizer(search_space)
-    opt.search(objective_function, n_iter=30)
+    opt.search(test_function.objective_function, n_iter=30)
 
 
 ############################################################
@@ -75,7 +75,7 @@ def test_optimization_2D(objective_function):
 
 
 objective_function_para_3D = (
-    "objective_function",
+    "test_function",
     [
         (sphere_function),
         (rastrigin_function),
@@ -85,7 +85,7 @@ def test_optimization_2D(objective_function):
 
 
 @pytest.mark.parametrize(*objective_function_para_3D)
-def test_optimization_3D(objective_function):
+def test_optimization_3D(test_function):
     search_space = {
         "x0": np.arange(0, 100, 1),
         "x1": np.arange(0, 100, 1),
@@ -93,7 +93,7 @@ def test_optimization_3D(objective_function):
     }
 
     opt = RandomSearchOptimizer(search_space)
-    opt.search(objective_function, n_iter=30)
+    opt.search(test_function.objective_function, n_iter=30)
 
 
 ############################################################
@@ -104,7 +104,7 @@ def test_optimization_3D(objective_function):
 
 
 objective_function_para_4D = (
-    "objective_function",
+    "test_function",
     [
         (sphere_function),
         (rastrigin_function),
@@ -114,7 +114,7 @@ def test_optimization_3D(objective_function):
 
 
 @pytest.mark.parametrize(*objective_function_para_4D)
-def test_optimization_4D(objective_function):
+def test_optimization_4D(test_function):
     search_space = {
         "x0": np.arange(0, 100, 1),
         "x1": np.arange(0, 100, 1),
@@ -123,4 +123,4 @@ def test_optimization_4D(objective_function):
     }
 
     opt = RandomSearchOptimizer(search_space)
-    opt.search(objective_function, n_iter=30)
+    opt.search(test_function.objective_function, n_iter=30)