diff --git a/tests/test_data_balance_of.py b/tests/test_data_balance_of.py
new file mode 100644
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+++ b/tests/test_data_balance_of.py
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+"""Test data.balance_of function"""
+# 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/>.
+
+from decimal import Decimal
+
+import pytest
+
+from . import testutil
+
+from conservancy_beancount import data
+
+@pytest.fixture
+def payable_payment_txn():
+    return testutil.Transaction(postings=[
+        ('Liabilities:Payable:Accounts', 50),
+        ('Assets:Checking', -50),
+        ('Expenses:BankingFees', 5),
+        ('Assets:Checking', -5),
+    ])
+
+@pytest.fixture
+def none_posting_txn():
+    return testutil.Transaction(postings=[
+        ('Income:Donations', -30),
+        ('Expenses:BankingFees', 3),
+        ('Assets:Checking', None),
+    ])
+
+@pytest.fixture
+def multipost_one_none_txn():
+    return testutil.Transaction(postings=[
+        ('Liabilities:Payable:Accounts', 50),
+        ('Assets:Checking', -50),
+        ('Expenses:BankingFees', 5),
+        ('Assets:Checking', None),
+    ])
+
+def test_balance_of_simple_txn():
+    txn = testutil.Transaction(postings=[
+        ('Assets:Cash', 50),
+        ('Income:Donations', -50),
+    ])
+    assert data.balance_of(txn, 'Assets') == 50
+    assert data.balance_of(txn, 'Income') == -50
+
+def test_zero_balance_of(payable_payment_txn):
+    assert data.balance_of(payable_payment_txn, 'Equity') == 0
+    assert data.balance_of(payable_payment_txn, 'Assets:Cash') == 0
+    assert data.balance_of(payable_payment_txn, 'Liabilities:CreditCard') == 0
+
+def test_balance_of_multipost_txn(payable_payment_txn):
+    assert data.balance_of(payable_payment_txn, 'Assets') == -55
+
+def test_multiarg_balance_of(payable_payment_txn):
+    assert data.balance_of(payable_payment_txn, 'Assets', 'Expenses') == -50
+    assert data.balance_of(payable_payment_txn, 'Assets', 'Liabilities') == -5
+
+def test_balance_of_uses_whole_account_names(payable_payment_txn):
+    assert data.balance_of(payable_payment_txn, 'Assets:Check') == 0
+
+def test_balance_of_none_posting(none_posting_txn):
+    assert data.balance_of(none_posting_txn, 'Assets') is None
+
+def test_balance_of_none_posting_with_default(none_posting_txn):
+    expected = Decimal('Infinity')
+    assert data.balance_of(none_posting_txn, 'Assets', default=expected) == expected
+
+def test_balance_of_other_side_of_none_posting(none_posting_txn):
+    assert data.balance_of(none_posting_txn, 'Income') == -30
+    assert data.balance_of(none_posting_txn, 'Expenses') == 3
+
+def test_balance_of_multi_postings_one_none(multipost_one_none_txn):
+    assert data.balance_of(multipost_one_none_txn, 'Assets') is None
+
+def test_balance_of_multi_postings_one_none(multipost_one_none_txn):
+    expected = Decimal('Infinity')
+    assert data.balance_of(multipost_one_none_txn, 'Assets', default=expected) == expected