diff --git a/km3io/tools.py b/km3io/tools.py
index 22bf1e64ab43ce233dd0d50a4fd47a51af4b24a7..045c0cb9f9c1daea57ee616aaf4aa08a4eeab39a 100644
--- a/km3io/tools.py
+++ b/km3io/tools.py
@@ -306,7 +306,7 @@ def best_track(events, strategy="default", rec_type=None, rec_stages=None):
         raise ValueError("{} not in {}".format(strategy, options))
 
     n_events = len(events)
-    if n_events>1 and any(events.n_tracks == 0):
+    if n_events > 1 and any(events.n_tracks == 0):
         raise ValueError(
             "'events' should not contain empty tracks. Consider applying the mask: events.n_tracks>0"
         )
diff --git a/tests/test_tools.py b/tests/test_tools.py
index 17f1fd1aee6f490980a9782dabd35a036530e816..05dd386eb69a1ca5454b483f42df62d93e6e142c 100644
--- a/tests/test_tools.py
+++ b/tests/test_tools.py
@@ -8,7 +8,8 @@ from pathlib import Path
 from km3io import OfflineReader
 from km3io.tools import (to_num, cached_property, unfold_indices, unique,
                          uniquecount, fitinf, fitparams, count_nested, _find,
-                         mask, best_track, rec_types, get_w2list_param, get_multiplicity)
+                         mask, best_track, rec_types, get_w2list_param,
+                         get_multiplicity)
 
 SAMPLES_DIR = Path(__file__).parent / 'samples'
 OFFLINE_FILE = OfflineReader(SAMPLES_DIR / 'km3net_offline.root')
@@ -90,11 +91,13 @@ class TestBestTrack(unittest.TestCase):
 
 class TestGetMultiplicity(unittest.TestCase):
     def test_get_multiplicity(self):
-        rec_stages_tracks = get_multiplicity(OFFLINE_FILE.events.tracks, [1, 3, 5, 4])
+        rec_stages_tracks = get_multiplicity(OFFLINE_FILE.events.tracks,
+                                             [1, 3, 5, 4])
 
         assert rec_stages_tracks.rec_stages[0] == [1, 3, 5, 4]
         assert rec_stages_tracks.rec_stages[1] == [1, 3, 5, 4]
 
+
 class TestCountNested(unittest.TestCase):
     def test_count_nested(self):
         fit = OFFLINE_FILE.events.tracks.fitinf