diff --git a/tardis/spectrum/tests/test_spectrum_solver.py b/tardis/spectrum/tests/test_spectrum_solver.py
index bb82e5d822c..941a34eefa0 100644
--- a/tardis/spectrum/tests/test_spectrum_solver.py
+++ b/tardis/spectrum/tests/test_spectrum_solver.py
@@ -32,9 +32,10 @@ def simulation(
         simulation.run_final()
 
         request.cls.regression_data = RegressionData(request)
-        request.cls.regression_data.sync_hdf_store(simulation)
+        data = request.cls.regression_data.sync_hdf_store(simulation)
 
-        return simulation
+        yield simulation
+        data.close()
 
     def get_expected_data(self, key: str):
         return pd.read_hdf(self.regression_data.fpath, key)
diff --git a/tardis/tests/fixtures/regression_data.py b/tardis/tests/fixtures/regression_data.py
index 064d33ef1f9..f25aa86d96b 100644
--- a/tardis/tests/fixtures/regression_data.py
+++ b/tardis/tests/fixtures/regression_data.py
@@ -24,6 +24,7 @@ def __init__(self, request) -> None:
             "--generate-reference"
         )
         self.fname = f"{self.fname_prefix}.UNKNOWN_FORMAT"
+        self.hdf_store_object = None
 
     @property
     def module_name(self):
@@ -161,9 +162,14 @@ def sync_hdf_store(self, tardis_module, update_fname=True):
                 f"Skipping test to generate regression data: {self.fpath}"
             )
         else:
-            return pd.HDFStore(self.fpath, mode="r")
-
+            # since each test function has its own regression data instance
+            # each test function will only have one HDFStore object
+            self.hdf_store_object = pd.HDFStore(self.fpath, mode="r")
+            return self.hdf_store_object
 
 @pytest.fixture(scope="function")
 def regression_data(request):
-    return RegressionData(request)
+    regression_data_instance = RegressionData(request)
+    yield regression_data_instance
+    if regression_data_instance.hdf_store_object is not None and regression_data_instance.hdf_store_object.is_open:
+        regression_data_instance.hdf_store_object.close()
diff --git a/tardis/tests/test_tardis_full.py b/tardis/tests/test_tardis_full.py
index 92a6a6fba4c..80ac724a84d 100644
--- a/tardis/tests/test_tardis_full.py
+++ b/tardis/tests/test_tardis_full.py
@@ -55,9 +55,10 @@ def simulation(
         simulation.run_final()
 
         request.cls.regression_data = RegressionData(request)
-        request.cls.regression_data.sync_hdf_store(simulation)
+        data = request.cls.regression_data.sync_hdf_store(simulation)
 
-        return simulation
+        yield simulation
+        data.close()
 
     def get_expected_data(self, key: str):
         return pd.read_hdf(self.regression_data.fpath, key)
diff --git a/tardis/tests/test_tardis_full_formal_integral.py b/tardis/tests/test_tardis_full_formal_integral.py
index c981c46f097..ca3024047ff 100644
--- a/tardis/tests/test_tardis_full_formal_integral.py
+++ b/tardis/tests/test_tardis_full_formal_integral.py
@@ -73,7 +73,8 @@ def simulation(self, config, atomic_data_fname):
     def test_simulation(self, simulation, request):
         regression_data = RegressionData(request)
         container = SimulationContainer(simulation)
-        regression_data.sync_hdf_store(container)
+        data = regression_data.sync_hdf_store(container)
+        data.close()
 
     def test_j_blue_estimators(self, simulation, request):
         regression_data = RegressionData(request)
diff --git a/tardis/visualization/tools/tests/test_liv_plot.py b/tardis/visualization/tools/tests/test_liv_plot.py
index 5a4f56897bc..ae50f66f8ee 100644
--- a/tardis/visualization/tools/tests/test_liv_plot.py
+++ b/tardis/visualization/tools/tests/test_liv_plot.py
@@ -357,6 +357,7 @@ def test_generate_plot_mpl(
                             + str(index2)
                         ),
                     )
+        expected.close()
 
     def test_mpl_image(self, plotter_generate_plot_mpl, tmp_path, request):
         """
@@ -520,3 +521,4 @@ def test_generate_plot_ply(
                 rtol=0.3,
                 atol=3,
             )
+        expected.close()
diff --git a/tardis/visualization/tools/tests/test_sdec_plot.py b/tardis/visualization/tools/tests/test_sdec_plot.py
index 1136ba7e148..2a11b00289d 100644
--- a/tardis/visualization/tools/tests/test_sdec_plot.py
+++ b/tardis/visualization/tools/tests/test_sdec_plot.py
@@ -231,6 +231,7 @@ def test_calculate_plotting_data(
                 pd.testing.assert_frame_equal(
                     plot_object, expected.get(group + attribute_name)
                 )
+        expected.close()
 
     @pytest.fixture(scope="class", params=combinations)
     def plotter_generate_plot_mpl(self, request, observed_spectrum, plotter):
@@ -331,6 +332,7 @@ def test_generate_plot_mpl(
                             + str(index2)
                         ),
                     )
+        expected.close()
 
     @pytest.fixture(scope="class", params=combinations)
     def plotter_generate_plot_ply(self, request, observed_spectrum, plotter):
@@ -416,6 +418,8 @@ def test_generate_plot_mpl(
                 data.y, expected.get(group + "y").values.flatten()
             )
 
+        expected.close()
+
     def test_mpl_image(self, plotter_generate_plot_mpl, tmp_path, request):
         regression_data = RegressionData(request)
         fig, _ = plotter_generate_plot_mpl