diff --git a/tests/metrics/__init__.py b/tests/metrics/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/metrics/tools/__init__.py b/tests/metrics/tools/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/metrics/tools/test_dates.py b/tests/metrics/tools/test_dates.py
new file mode 100644
index 00000000..28305cdf
--- /dev/null
+++ b/tests/metrics/tools/test_dates.py
@@ -0,0 +1,50 @@
+from datetime import date, datetime
+
+import pytest
+
+from metrics.tools.dates import date_from_iso, datetime_from_iso, iter_days
+
+
+@pytest.mark.parametrize(
+    "value,expected",
+    [
+        (None, None),
+        ("2020-07-08", date(2020, 7, 8)),
+        ("2020-07-08T09:12", date(2020, 7, 8)),
+    ],
+)
+def test_date_from_iso(value, expected):
+    assert date_from_iso(value) == expected
+
+
+@pytest.mark.parametrize(
+    "value,expected",
+    [
+        (None, None),
+        ("2020-07-08", datetime(2020, 7, 8, 0, 0, 0)),
+        ("2020-07-08T09:12", datetime(2020, 7, 8, 9, 12, 0)),
+    ],
+)
+def test_datetime_from_iso(value, expected):
+    assert datetime_from_iso(value) == expected
+
+
+def test_iter_days():
+    dates = list(iter_days(date(2020, 7, 8), date(2020, 7, 10)))
+
+    assert dates == [
+        date(2020, 7, 8),
+        date(2020, 7, 9),
+        date(2020, 7, 10),
+    ]
+
+
+def test_iter_days_with_empty_values():
+    with pytest.raises(TypeError):
+        list(iter_days(None, date(2020, 7, 8)))
+
+    with pytest.raises(TypeError):
+        list(iter_days(date(2020, 7, 8), None))
+
+    with pytest.raises(TypeError):
+        list(iter_days(date(2020, 7, 8), date(2022, 7, 8), None))