diff --git a/billing/tests/test_accounts.py b/billing/tests/test_accounts.py
new file mode 100644
index 0000000000..6960c5af93
--- /dev/null
+++ b/billing/tests/test_accounts.py
@@ -0,0 +1,61 @@
+import unittest
+
+from billing.accounts import BankAccount
+
+
+class TestBankAccount(unittest.TestCase):
+    def setUp(self):
+        self.account = BankAccount("John Doe", 100.0)
+
+    def test_init(self):
+        self.assertEqual(self.account.owner, "John Doe")
+        self.assertEqual(self.account.balance, 100.0)
+        with self.assertRaises(ValueError):
+            BankAccount("Jane Doe", -50.0)
+
+    def test_deposit(self):
+        new_balance = self.account.deposit(50.0)
+        self.assertEqual(new_balance, 150.0)
+        self.assertEqual(self.account.balance, 150.0)
+        with self.assertRaises(ValueError):
+            self.account.deposit(-10.0)
+        with self.assertRaises(ValueError):
+            self.account.deposit(0)
+
+    def test_withdraw(self):
+        new_balance = self.account.withdraw(50.0)
+        self.assertEqual(new_balance, 50.0)
+        self.assertEqual(self.account.balance, 50.0)
+        with self.assertRaises(ValueError):
+            self.account.withdraw(-10.0)
+        with self.assertRaises(ValueError):
+            self.account.withdraw(0)
+        with self.assertRaises(ValueError):
+            self.account.withdraw(1000.0)
+
+    def test_transfer(self):
+        other_account = BankAccount("Jane Doe", 50.0)
+        balances = self.account.transfer(other_account, 30.0)
+        self.assertEqual(balances, (70.0, 80.0))
+        self.assertEqual(self.account.balance, 70.0)
+        self.assertEqual(other_account.balance, 80.0)
+
+        with self.assertRaises(ValueError):
+            self.account.transfer(other_account, -10.0)
+        with self.assertRaises(ValueError):
+            self.account.transfer(other_account, 0)
+        with self.assertRaises(ValueError):
+            self.account.transfer(other_account, 1000.0)
+        with self.assertRaises(ValueError):
+            self.account.transfer("not an account", 10.0)
+
+    def test_get_balance(self):
+        self.assertEqual(self.account.get_balance(), 100.0)
+        self.account.deposit(50.0)
+        self.assertEqual(self.account.get_balance(), 150.0)
+        self.account.withdraw(30.0)
+        self.assertEqual(self.account.get_balance(), 120.0)
+
+
+if __name__ == "__main__":
+    unittest.main()