diff --git a/src/openmc_source_plotter/core.py b/src/openmc_source_plotter/core.py
index 2a056f4..6392b26 100644
--- a/src/openmc_source_plotter/core.py
+++ b/src/openmc_source_plotter/core.py
@@ -98,7 +98,7 @@ def plot_source_energy(
         xaxis_units: The units to use for the x axis. Options are 'eV' or 'MeV'.
     """
 
-    if xaxis_units not in ['eV', 'MeV']:
+    if xaxis_units not in ["eV", "MeV"]:
         raise ValueError(f"xaxis_units must be either 'eV' or 'MeV' not {xaxis_units}")
 
     if figure is None:
@@ -121,8 +121,8 @@ def plot_source_energy(
     if isinstance(self, openmc.SourceBase):
         probability = probability * self.strength
     energy = bin_edges[:-1]
-    if xaxis_units == 'MeV':
-        energy = energy /1e6
+    if xaxis_units == "MeV":
+        energy = energy / 1e6
     # Plot source energy histogram
     figure.add_trace(
         plotly.graph_objects.Scatter(
diff --git a/tests/test_core_with_source.py b/tests/test_core_with_source.py
index 1b9e0cc..ed54bf0 100644
--- a/tests/test_core_with_source.py
+++ b/tests/test_core_with_source.py
@@ -47,9 +47,14 @@ def test_energy_plot(test_source):
     assert isinstance(plot, go.Figure)
     assert len(plot.data[0]["x"]) == 1
 
+
 def test_energy_plot_axis(test_source):
-    plot = test_source.plot_source_energy(n_samples=10, xaxis_type='log', yaxis_type='linear', xaxis_units='eV')
-    plot = test_source.plot_source_energy(n_samples=10, xaxis_type='linear', yaxis_type='log', xaxis_units='MeV')
+    plot = test_source.plot_source_energy(
+        n_samples=10, xaxis_type="log", yaxis_type="linear", xaxis_units="eV"
+    )
+    plot = test_source.plot_source_energy(
+        n_samples=10, xaxis_type="linear", yaxis_type="log", xaxis_units="MeV"
+    )
     assert isinstance(plot, go.Figure)
     assert len(plot.data[0]["x"]) == 1