diff --git a/requirements-dev.txt b/requirements-dev.txt
index 6e98953..ae69777 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -2,7 +2,6 @@
 
 black~=23.7.0
 isort~=5.12.0
-matplotlib>=3.5.1
 mypy~=1.7.1
 pandas-stubs
 pytest-cov
diff --git a/src/antares/tsgen/ts_generator.py b/src/antares/tsgen/ts_generator.py
index 83ac224..438dff7 100644
--- a/src/antares/tsgen/ts_generator.py
+++ b/src/antares/tsgen/ts_generator.py
@@ -128,9 +128,7 @@ def _check_cluster(cluster: ThermalCluster) -> None:
 
     _check_array(cluster.modulation < 0, "Hourly modulation is negative on following hours")
 
-    lengths = _check_lengths(cluster.outage_gen_params)
-    if len(lengths) != 1:
-        raise ValueError(f"Not all daily arrays have same size, got {lengths}")
+    _check_lengths(cluster.outage_gen_params)
 
 
 def _check_link_capacity(link_capacity: LinkCapacity) -> None:
@@ -148,13 +146,10 @@ def _check_link_capacity(link_capacity: LinkCapacity) -> None:
     _check_array(link_capacity.modulation_direct < 0, "Hourly direct modulation is negative on following hours")
     _check_array(link_capacity.modulation_indirect < 0, "Hourly indirect modulation is negative on following hours")
 
-    lengths = _check_lengths(link_capacity.outage_gen_params)
-
-    if len(lengths) != 1:
-        raise ValueError(f"Not all daily arrays have same size, got {lengths}")
+    _check_lengths(link_capacity.outage_gen_params)
 
 
-def _check_lengths(outage_gen_params: OutageGenerationParameters) -> set[int]:
+def _check_lengths(outage_gen_params: OutageGenerationParameters) -> None:
     lengths = {
         len(a)
         for a in [
@@ -166,7 +161,9 @@ def _check_lengths(outage_gen_params: OutageGenerationParameters) -> set[int]:
             outage_gen_params.npo_max,
         ]
     }
-    return lengths
+
+    if len(lengths) != 1:
+        raise ValueError(f"Not all daily arrays have same size, got {lengths}")
 
 
 class OutageOutput:
diff --git a/tests/test_duration_generator.py b/tests/test_duration_generator.py
index 34b1d9e..14dd0a9 100644
--- a/tests/test_duration_generator.py
+++ b/tests/test_duration_generator.py
@@ -10,7 +10,6 @@
 #
 # This file is part of the Antares project.
 
-import matplotlib.pyplot as plt
 import pytest
 
 from antares.tsgen.duration_generator import (