diff --git a/.github/workflows/python-tests.yml b/.github/workflows/python-tests.yml
new file mode 100644
index 0000000..af5abac
--- /dev/null
+++ b/.github/workflows/python-tests.yml
@@ -0,0 +1,30 @@
+name: Python package
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.8", "3.10"]
+
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v4
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        # This case we are only updating pip, but you could add other dependencies needed.
+        run: |
+          python -m pip install --upgrade pip
+          pip install pytest
+          pip install pytest-cov
+      - name: Test with pytest
+        run: |
+          pytest
+      - name: Test coverage
+        run: |
+          pytest --cov
\ No newline at end of file
diff --git a/test_times.py b/test_times.py
new file mode 100644
index 0000000..beacb28
--- /dev/null
+++ b/test_times.py
@@ -0,0 +1,62 @@
+from times import compute_overlap_time, time_range
+from pytest import raises
+import pytest
+
+# def test_given_input():
+#     outer = time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00")
+#     inner = time_range("2010-01-12 10:30:00", "2010-01-12 10:45:00", 2, 60)
+#     result = compute_overlap_time(outer, inner)
+#     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_nooverlap():
+#     first = time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00")
+#     second = time_range("2010-01-12 09:30:00", "2010-01-12 09:45:00")
+#     result = compute_overlap_time(first, second)
+#     expected = []
+#     assert result == expected
+
+# def test_multipleintervals():
+#     first = time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00", 3, 10)
+#     second = time_range("2010-01-12 10:30:00", "2010-01-12 10:45:00", 2, 60)
+#     result = compute_overlap_time(first, second)
+#     expected = [('2010-01-12 10:30:00', '2010-01-12 10:37:00'), ('2010-01-12 10:38:00', '2010-01-12 10:39:53'), ('2010-01-12 10:40:03', '2010-01-12 10:45:00')]
+#     assert result == expected
+
+# def test_border():
+#     first = time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00")
+#     second = time_range("2010-01-12 12:00:00", "2010-01-12 12:45:00")
+#     result = compute_overlap_time(first, second)
+#     expected = [('2010-01-12 12:00:00', '2010-01-12 12:00:00')]
+#     assert result == expected
+
+def test_backwardsrange():
+    with raises(ValueError):
+        range = time_range("2010-01-12 14:00:00", "2010-01-12 12:00:00")
+
+test_cases = [
+    #given input
+    (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')]),
+
+    #no overlap
+    (time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00"),
+     time_range("2010-01-12 09:30:00", "2010-01-12 09:45:00"),
+     []),
+
+    #multiple intervals each
+    (time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00", 3, 10),
+     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 10:39:53'), ('2010-01-12 10:40:03', '2010-01-12 10:45:00')]),
+
+    #border case
+    (time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00"),
+     time_range("2010-01-12 12:00:00", "2010-01-12 12:45:00"),
+     [('2010-01-12 12:00:00', '2010-01-12 12:00:00')])
+]
+
+@pytest.mark.parametrize("time_range1, time_range2, expected", test_cases)
+def test_timeranges(time_range1, time_range2, expected):
+    result = compute_overlap_time(time_range1, time_range2)
+    assert result == expected
\ No newline at end of file
diff --git a/times.py b/times.py
index d57f401..4751e0d 100644
--- a/times.py
+++ b/times.py
@@ -4,6 +4,8 @@
 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")
+    if start_time_s > end_time_s:
+        raise ValueError('Start time needs to be before the 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))
@@ -17,10 +19,11 @@ 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__":
+if __name__ == "__main__": #this will only be executed when file is run directly, not imported
     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