diff --git a/.github/workflows/python-tests.yml b/.github/workflows/python-tests.yml
new file mode 100644
index 0000000..a29462c
--- /dev/null
+++ b/.github/workflows/python-tests.yml
@@ -0,0 +1,28 @@
+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
+          python -m pip install pytest
+          python -m pip install pytest-cov
+      - name: Test with pytest
+        run: |
+          pytest
+          pytest --cov="."
\ No newline at end of file
diff --git a/test_times.py b/test_times.py
new file mode 100644
index 0000000..d035c01
--- /dev/null
+++ b/test_times.py
@@ -0,0 +1,44 @@
+from times import *
+import pytest
+
+def test_given_input():
+    """Standard results"""
+    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():
+    """Two time ranges that do not overlap"""
+    large = time_range("2010-01-12 10:00:00", "2010-01-12 12:00:00")
+    short = time_range("2010-01-12 12:30:00", "2010-01-12 12:45:00")
+    result = compute_overlap_time(large, short)
+    expected = []
+    assert result == expected
+
+def test_several_intervals():
+    """Two time ranges that both contain several intervals each"""
+    large = time_range("2010-01-12 10:00:00", "2010-01-12 10:31:00", 2, 60) #10-15 16-31
+    short = time_range("2010-01-12 10:15:00", "2010-01-12 10:46:00", 2, 60) #15-30 31-46
+    result = compute_overlap_time(large, short)
+    expected = [('2010-01-12 10:15:00', '2010-01-12 10:15:00'), ('2010-01-12 10:16:00', '2010-01-12 10:30:00'), ('2010-01-12 10:31:00', '2010-01-12 10:31:00')]
+    assert result == expected
+
+def test_end_to_end():
+    """Two time ranges that end exactly at the same time when the other starts"""
+    large = time_range("2010-01-12 10:00:00", "2010-01-12 10:31:00")
+    short = time_range("2010-01-12 10:31:00", "2010-01-12 10:46:00")
+    result = compute_overlap_time(large, short)
+    expected = [('2010-01-12 10:31:00', '2010-01-12 10:31:00')]
+    assert result == expected
+
+def test_time_range_backwards():
+    with pytest.raises(ValueError, match=r"End time: .* is before start time: .*\."):
+        time_range("2010-01-12 10:45:00", "2010-01-12 10:31:00")
+
+"""
+For test coverage, run in terminal:
+pytest --cov="." --cov-report html
+python -m http.server -d htmlcov
+"""
\ No newline at end of file
diff --git a/times.py b/times.py
index d57f401..e53766d 100644
--- a/times.py
+++ b/times.py
@@ -1,9 +1,11 @@
-import datetime
+import datetime 
 
 
 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(f"End time: {end_time} is before start time: {start_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))
@@ -17,7 +19,8 @@ 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__":