diff --git a/.github/workflows/unit_tests.yml b/.github/workflows/unit_tests.yml
index dade360..bb98266 100644
--- a/.github/workflows/unit_tests.yml
+++ b/.github/workflows/unit_tests.yml
@@ -15,7 +15,7 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-latest, windows-latest, macos-latest ]
-        python-version: [ "3.11" ]
+        python-version: [ "3.9", "3.10", "3.11" ]
 
     steps:
       - uses: actions/checkout@v3
@@ -35,9 +35,9 @@ jobs:
       - name: Lint with ruff
         run: |
           # stop the build if there are Python syntax errors or undefined names
-          ruff --format=github --select=E9,F63,F7,F82 --target-version=py37 .
+          ruff --output-format=github --select=E9,F63,F7,F82 --target-version=py37 .
           # default set of ruff rules with GitHub Annotations
-          ruff --format=github --target-version=py37 .
+          ruff --output-format=github --target-version=py37 .
         continue-on-error: true
       - name: List files in workspace
         run: |
@@ -48,14 +48,14 @@ jobs:
         run: |
           coverage run -m pytest tests/
           coverage xml -o coverage.xml
-      - name: Upload coverage report (only for ubuntu-latest and python 3.11)
-        if: ${{ matrix.os == 'ubuntu-latest' && matrix.python-version == '3.11' }}
+      - name: Upload coverage report (only for ubuntu-latest and python 3.10)
+        if: ${{ matrix.os == 'ubuntu-latest' && matrix.python-version == '3.10' }}
         uses: actions/upload-artifact@v3
         with:
           name: coverage-report
           path: coverage.xml
-      - name: Run Coveralls (only for ubuntu-latest and python 3.11)
-        if: ${{ matrix.os == 'ubuntu-latest' && matrix.python-version == '3.11' }}
+      - name: Run Coveralls (only for ubuntu-latest and python 3.10)
+        if: ${{ matrix.os == 'ubuntu-latest' && matrix.python-version == '3.10' }}
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         uses: coverallsapp/github-action@v2
diff --git a/eventdetector_ts/optimization/event_extraction_pipeline.py b/eventdetector_ts/optimization/event_extraction_pipeline.py
index cb9379e..522d696 100644
--- a/eventdetector_ts/optimization/event_extraction_pipeline.py
+++ b/eventdetector_ts/optimization/event_extraction_pipeline.py
@@ -20,8 +20,8 @@ class OptimizationData:
         - time_unit (TimeUnit): Unit of time used in the dataset.
         - true_events (pd.DataFrame): DataFrame to store true events.
         - predicted_op (np.ndarray): Array to store predicted outcomes.
-        - delta Union[int, float]: The maximum time tolerance used to determine the correspondence between a predicted event
-                    and its actual counterpart in the true events.
+        - delta Union[int, float]: The maximum time tolerance used to determine the correspondence between a predicted 
+            event and its actual counterpart in the true events.
         - s_h (float): A step parameter for the peak height threshold h.
         - s_s (int): Step size in time unit for overlapping the partition.
         - w_s (int): Size in time unit of the overlapping partition.
@@ -44,8 +44,8 @@ def __init__(self, t_max: float, w_s: int, s_s: int,
             w_s (int): Size in time unit of the overalapping partition.
             s_s (int): Step size in time unit for overalapping the partition.
             s_h (float): A step parameter for the peak height threshold h.
-            delta Union[int, float]: The maximum time tolerance used to determine the correspondence between a predicted event
-                    and its actual counterpart in the true events.
+            delta Union[int, float]: The maximum time tolerance used to determine the correspondence between a predicted
+                event and its actual counterpart in the true events.
             output_dir (str): The parent directory.
             time_unit (TimeUnit): Unit of time used in the dataset.
         """
diff --git a/eventdetector_ts/plotter/plotter.py b/eventdetector_ts/plotter/plotter.py
index 0ffaf4c..a1dbf71 100644
--- a/eventdetector_ts/plotter/plotter.py
+++ b/eventdetector_ts/plotter/plotter.py
@@ -165,7 +165,7 @@ def plot_predicted_events(self) -> None:
                                        style=STYLE_PREDICTED)
             ax.add_patch(rect1)
 
-        for _, test_date in self.true_events[MIDDLE_EVENT_LABEL].iteritems():
+        for _, test_date in self.true_events[MIDDLE_EVENT_LABEL].items():
             rect1 = event_to_rectangle(event=test_date, width_events_s=self.width_events_s, time_unit=self.time_unit,
                                        color=COLOR_TRUE,
                                        style=STYLE_TRUE)