diff --git a/tests/test_ranges.py b/tests/test_ranges.py
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+++ b/tests/test_ranges.py
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+"""test_ranges.py - Unit tests for range classes"""
+# Copyright © 2020  Brett Smith
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import datetime
+
+import pytest
+
+from conservancy_beancount import ranges
+
+ONE_DAY = datetime.timedelta(days=1)
+
+@pytest.mark.parametrize('start,stop', [
+    # One month
+    (datetime.date(2018, 3, 1), datetime.date(2018, 4, 1)),
+    # Three months
+    (datetime.date(2018, 6, 1), datetime.date(2018, 9, 1)),
+    # Six months, spanning year
+    (datetime.date(2018, 9, 1), datetime.date(2019, 3, 1)),
+    # Nine months
+    (datetime.date(2018, 2, 1), datetime.date(2018, 12, 1)),
+    # Twelve months on Jan 1
+    (datetime.date(2018, 1, 1), datetime.date(2019, 1, 1)),
+    # Twelve months spanning year
+    (datetime.date(2018, 3, 1), datetime.date(2019, 3, 1)),
+    # Eighteen months spanning year
+    (datetime.date(2018, 3, 1), datetime.date(2019, 9, 1)),
+    # Wild
+    (datetime.date(2018, 1, 1), datetime.date(2020, 4, 15)),
+])
+def test_date_range(start, stop):
+    date_range = ranges.DateRange(start, stop)
+    assert (start - ONE_DAY) not in date_range
+    assert start in date_range
+    assert (start + ONE_DAY) in date_range
+    assert (stop - ONE_DAY) in date_range
+    assert stop not in date_range
+    assert (stop + ONE_DAY) not in date_range
+
+def test_date_range_one_day():
+    start = datetime.date(2018, 7, 1)
+    date_range = ranges.DateRange(start, start + ONE_DAY)
+    assert (start - ONE_DAY) not in date_range
+    assert start in date_range
+    assert (start + ONE_DAY) not in date_range
+
+def test_date_range_empty():
+    date = datetime.date(2018, 8, 10)
+    date_range = ranges.DateRange(date, date)
+    assert (date - ONE_DAY) not in date_range
+    assert date not in date_range
+    assert (date + ONE_DAY) not in date_range