diff --git a/.github/workflows/python-tests.yml b/.github/workflows/python-tests.yml
new file mode 100644
index 0000000..c39f350
--- /dev/null
+++ b/.github/workflows/python-tests.yml
@@ -0,0 +1,27 @@
+name: Python package
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.10", "3.13"]
+
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        # This case we are only updating pip, but you could add other dependencies if needed.
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install pytest
+          # ⚠️⚠️⚠️ FIXME Is there anything else that needs to be installed?
+      - name: Test with pytest
+        run: |
+          pytest
\ No newline at end of file
diff --git a/README.md b/README.md
index 72585a5..ee3a6dd 100644
--- a/README.md
+++ b/README.md
@@ -28,13 +28,13 @@ uv add --dev pytest
 > ```
 >
 > The `time_range` function generates the observation blocks for a given start and end time, a number of intervals and a duration for the gaps.  For the first row above, this would be:
-> `"2025-06-25 00:00:00", "2025-06-25 00:11:00", 2, 60`
+> `"2025-06-01 00:00:00", "2025-06-01 00:11:00", 2, 60`
 > and for the second:
 > `"2025-01-01 00:02:00", "2025-01-01 00:12:00", 4, 120`.  
 > And the `compute_overlap_time` should provide:
 > ```python
-> [('2020-01-01 00:02:00', '2020-01-01 00:03:00'),  # first interval
->  ('2020-01-01 00:08:00', '2020-01-01 00:09:00')]  # second interval 
+> [('2025-01-01 00:02:00', '2025-01-01 00:03:00'),  # first interval
+>  ('2025-01-01 00:08:00', '2025-01-01 00:09:00')]  # second interval 
 > ```
 
 ## Step 2: Writing a unit test
diff --git a/__pycache__/test_parametrize.cpython-313-pytest-8.4.1.pyc b/__pycache__/test_parametrize.cpython-313-pytest-8.4.1.pyc
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diff --git a/__pycache__/test_time.cpython-313-pytest-8.4.1.pyc b/__pycache__/test_time.cpython-313-pytest-8.4.1.pyc
new file mode 100644
index 0000000..f9ddc37
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diff --git a/__pycache__/times.cpython-313-pytest-8.4.1.pyc b/__pycache__/times.cpython-313-pytest-8.4.1.pyc
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index 0000000..f7d3717
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diff --git a/__pycache__/times.cpython-313.pyc b/__pycache__/times.cpython-313.pyc
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diff --git a/test_parametrize.py b/test_parametrize.py
new file mode 100644
index 0000000..ff381b3
--- /dev/null
+++ b/test_parametrize.py
@@ -0,0 +1,41 @@
+import pytest
+from times import time_range, compute_overlap_time
+
+
+@pytest.mark.parametrize(
+    "test_input1, test_input2, expected",
+    [
+        pytest.param(
+            time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00"),
+            time_range("2010-01-12 10:30:00", "2010-01-12 10:45:00", 2, 60),
+            [
+                ("2010-01-12 10:30:00", "2010-01-12 10:37:00"),
+                ("2010-01-12 10:38:00", "2010-01-12 10:45:00"),
+            ],
+            id="given input",
+        ),
+        pytest.param(
+            time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00"),
+            time_range("2010-01-13 10:30:00", "2010-01-13 10:45:00", 2, 60),
+            [],
+            id="no overlap",
+        ),
+        pytest.param(
+            time_range("2025-01-01 00:00:00", "2025-01-01 00:11:00", 2, 60),
+            time_range("2025-01-01 00:02:00", "2025-01-01 00:12:00", 4, 120),
+            [
+                ("2025-01-01 00:02:00", "2025-01-01 00:03:00"),
+                ("2025-01-01 00:08:00", "2025-01-01 00:09:00"),
+            ],
+            id="multiple intervals",
+        ),
+        pytest.param(
+            time_range("2025-06-25 00:00:00", "2025-06-25 00:11:00"),
+            time_range("2025-06-25 00:11:00", "2025-06-25 00:22:00"),
+            [],
+            id="edge case",
+        ),
+    ],
+)
+def test_eval(test_input1, test_input2, expected):
+    assert compute_overlap_time(test_input1, test_input2) == expected
diff --git a/test_time.py b/test_time.py
new file mode 100644
index 0000000..a8a76fd
--- /dev/null
+++ b/test_time.py
@@ -0,0 +1,48 @@
+from times import time_range, compute_overlap_time
+from pytest import raises
+
+
+def test_given_input():
+    large = time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00")
+    short = time_range("2010-01-12 10:30:00", "2010-01-12 10:45:00", 2, 60)
+    result = compute_overlap_time(large, short)
+    expected = [
+        ("2010-01-12 10:30:00", "2010-01-12 10:37:00"),
+        ("2010-01-12 10:38:00", "2010-01-12 10:45:00"),
+    ]
+
+    assert result == expected
+
+
+def test_no_overlap():
+    large = time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00")
+    short = time_range("2010-01-13 10:30:00", "2010-01-13 10:45:00", 2, 60)
+    result = compute_overlap_time(large, short)
+    expected = []
+
+    assert result == expected
+
+
+def test_multi_intervals():
+    large = time_range("2025-01-01 00:00:00", "2025-01-01 00:11:00", 2, 60)
+    short = time_range("2025-01-01 00:02:00", "2025-01-01 00:12:00", 4, 120)
+    result = compute_overlap_time(large, short)
+    print(result)
+    expected = [
+        ("2025-01-01 00:02:00", "2025-01-01 00:03:00"),
+        ("2025-01-01 00:08:00", "2025-01-01 00:09:00"),
+    ]
+    assert result == expected
+
+
+def test_edge_case():
+    first = time_range("2025-06-25 00:00:00", "2025-06-25 00:11:00")
+    second = time_range("2025-06-25 00:11:00", "2025-06-25 00:22:00")
+    result = compute_overlap_time(first, second)
+    expected = []
+    assert result == expected
+
+
+def test_start_ends():
+    with raises(ValueError, match=r"Start time must be before end time"):
+        time_range("2025-01-01 00:01:00", "2025-01-01 00:00:00")
diff --git a/times.py b/times.py
index d57f401..932a83e 100644
--- a/times.py
+++ b/times.py
@@ -4,11 +4,26 @@
 def time_range(start_time, end_time, number_of_intervals=1, gap_between_intervals_s=0):
     start_time_s = datetime.datetime.strptime(start_time, "%Y-%m-%d %H:%M:%S")
     end_time_s = datetime.datetime.strptime(end_time, "%Y-%m-%d %H:%M:%S")
-    d = (end_time_s - start_time_s).total_seconds() / number_of_intervals + gap_between_intervals_s * (1 / number_of_intervals - 1)
-    sec_range = [(start_time_s + datetime.timedelta(seconds=i * d + i * gap_between_intervals_s),
-                  start_time_s + datetime.timedelta(seconds=(i + 1) * d + i * gap_between_intervals_s))
-                 for i in range(number_of_intervals)]
-    return [(ta.strftime("%Y-%m-%d %H:%M:%S"), tb.strftime("%Y-%m-%d %H:%M:%S")) for ta, tb in sec_range]
+    if start_time_s > end_time_s:
+        raise ValueError("Start time must be before end time")
+    d = (
+        end_time_s - start_time_s
+    ).total_seconds() / number_of_intervals + gap_between_intervals_s * (
+        1 / number_of_intervals - 1
+    )
+    sec_range = [
+        (
+            start_time_s
+            + datetime.timedelta(seconds=i * d + i * gap_between_intervals_s),
+            start_time_s
+            + datetime.timedelta(seconds=(i + 1) * d + i * gap_between_intervals_s),
+        )
+        for i in range(number_of_intervals)
+    ]
+    return [
+        (ta.strftime("%Y-%m-%d %H:%M:%S"), tb.strftime("%Y-%m-%d %H:%M:%S"))
+        for ta, tb in sec_range
+    ]
 
 
 def compute_overlap_time(range1, range2):
@@ -17,10 +32,12 @@ def compute_overlap_time(range1, range2):
         for start2, end2 in range2:
             low = max(start1, start2)
             high = min(end1, end2)
-            overlap_time.append((low, high))
+            if low < high:
+                overlap_time.append((low, high))
     return overlap_time
 
+
 if __name__ == "__main__":
     large = time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00")
     short = time_range("2010-01-12 10:30:00", "2010-01-12 10:45:00", 2, 60)
-    print(compute_overlap_time(large, short))
\ No newline at end of file
+    print(compute_overlap_time(large, short))