diff --git a/.gitignore b/.gitignore
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diff --git a/week05-testing/test_times.py b/week05-testing/test_times.py
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+++ b/week05-testing/test_times.py
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+import pytest
+from times import compute_overlap_time, time_range
+
+
+@pytest.mark.parametrize("first_range, second_range, expected_overlap",
+[(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")]),
+  (time_range("2010-01-12 10:00:00", "2010-01-12 11:00:00"),
+  time_range("2010-01-12 12:30:00", "2010-01-12 12:45:00", 2, 60),
+  []),
+  (time_range("2010-01-12 10:00:00", "2010-01-12 13:00:00", 3, 900),
+  time_range("2010-01-12 10:40:00", "2010-01-12 11:20:00", 2, 120),
+  [("2010-01-12 10:40:00","2010-01-12 10:50:00"), ("2010-01-12 11:05:00", "2010-01-12 11:20:00")]),
+  (time_range("2010-01-12 10:00:00", "2010-01-12 11:00:00"),
+  time_range("2010-01-12 11:00:00", "2010-01-12 12:45:00"),
+  [])
+])
+def test_time_range_overlap(first_range, second_range, expected_overlap):
+    assert compute_overlap_time(first_range, second_range) == expected_overlap
+
+# two ways of doing the same negative test. Only one is needed.
+def test_negative_time_range():
+    # first possible solution
+    with pytest.raises(ValueError) as e:
+        time_range("2010-01-12 10:00:00", "2010-01-12 09:30:00")
+    # lines after the error is raised are not executed in the pytest.raises context, so the assertion has to be outside the "with"    
+    assert e.match('The end of the time range has to come strictly after its start.')
+    
+def test_negative_time_range_alternative():
+    # an alternative solution for using pytest.raises to check that the error message is as expected
+    expected_error_message = 'The end of the time range has to come strictly after its start.'
+    with pytest.raises(ValueError, match=expected_error_message):
+        time_range("2010-01-12 10:00:00", "2010-01-12 09:30:00")
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diff --git a/week05-testing/times.py b/week05-testing/times.py
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+++ b/week05-testing/times.py
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+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('The end of the time range has to come strictly after its start.')
+    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):
+    overlap_time = []
+    for start1, end1 in range1:
+        for start2, end2 in range2:
+            # both ranges need to start before the other ends, otherwise there is no overlap!
+            if start1 <= end2 and start2 <= end1: 
+                low = max(start1, start2)
+                high = min(end1, end2)
+                if high == low:
+                    continue
+                overlap_time.append((low, high))
+    return overlap_time
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