initial commit

README.md

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+# Session 9 - Banking Unit Tests (PyTest)
+
+A small local Python project aligned with the Session 9 lecture. It includes conditional banking functions, BVA parametrization, negative tests with `pytest.raises`, a `yield` fixture in `conftest.py`, and a mock of the external notification dependency.
+
+## Run locally
+
+From the project folder:
+
+```bash
+python -m venv .venv
+```
+
+Activate the virtual environment:
+
+- Windows PowerShell: `.venv\Scripts\Activate.ps1`
+- macOS/Linux: `source .venv/bin/activate`
+
+Install dependencies and run tests:
+
+```bash
+python -m pip install -r requirements.txt
+python -m pytest -v
+python -m pytest --cov=banking --cov-branch --cov-report=term-missing --cov-report=html
+```
+
+Open `htmlcov/index.html` for the detailed coverage report. The included `coverage_report.txt` contains a verified sample run. No deployment, database, or real notification service is needed.
+
+## Lecture checklist
+
+- Three conditional operations: `deposit`, `withdraw`, `transfer` (plus constructor validation)
+- At least eight test cases, including parametrized boundary values
+- Multiple negative `pytest.raises` tests
+- `yield` fixture with cleanup in `tests/conftest.py`
+- `unittest.mock.patch` on `banking.send_notification` (where it is used)
+- Statement and branch coverage with a short analysis
+
+Amounts use integer units to avoid floating-point money rounding in this introductory example. `notification_service.py` deliberately raises if called directly: unit tests mock this external dependency. The transfer example is in-memory and not intended as a production banking implementation.

banking.py

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+from notification_service import send_notification
+
+
+class BankAccount:
+    def __init__(self, owner, balance=0):
+        if not owner.strip():
+            raise ValueError("Owner is required")
+        if balance < 0:
+            raise ValueError("Initial balance cannot be negative")
+        self.owner = owner
+        self.balance = balance
+
+    def deposit(self, amount):
+        if amount <= 0:
+            raise ValueError("Deposit must be positive")
+        self.balance += amount
+        return self.balance
+
+    def withdraw(self, amount):
+        if amount <= 0:
+            raise ValueError("Withdrawal must be positive")
+        if amount > self.balance:
+            raise ValueError("Insufficient funds")
+        self.balance -= amount
+        return self.balance
+
+    def transfer(self, recipient, amount):
+        if recipient is self:
+            raise ValueError("Cannot transfer to the same account")
+        if amount <= 0:
+            raise ValueError("Transfer must be positive")
+        if amount > self.balance:
+            raise ValueError("Insufficient funds")
+        self.balance -= amount
+        recipient.balance += amount
+        send_notification(recipient.owner, f"Received {amount} from {self.owner}")
+        return self.balance

coverage_analysis.md

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+# Coverage report and analysis
+
+Command: `python -m pytest --cov=banking --cov-branch --cov-report=term-missing --cov-report=html`
+
+Verified run: **17 passed**. `banking.py`: 32 statements, 0 missed; 16 branches, 0 partial; total coverage **100%**.
+
+No conditional branches in `banking.py` remain uncovered. The tests exercise valid operations, boundary values, invalid amounts, insufficient funds, self-transfer, and invalid constructor inputs. The notification is patched at `banking.send_notification`, so the tests verify its invocation without calling the real external dependency. `notification_service.py` is intentionally excluded from `--cov=banking` because this is a unit test of the banking module, not an integration test of the external service.
+
+Coverage measures execution, not proof of correctness; production banking would require additional integration, persistence, concurrency, and transaction-failure tests.

coverage_report.txt

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+============================= test session starts ==============================
+platform linux -- Python 3.13.5, pytest-9.0.2, pluggy-1.6.0 -- /opt/pyvenv/bin/python
+cachedir: .pytest_cache
+metadata: {'Python': '3.13.5', 'Platform': 'Linux-6.18.55-x86_64-with-glibc2.41', 'Packages': {'pytest': '9.0.2', 'pluggy': '1.6.0'}, 'Plugins': {'anyio': '4.13.0', 'ddtrace': '4.4.0', 'Faker': '40.1.2', 'asyncio': '1.3.0', 'cov': '7.0.0', 'json-report': '1.5.0', 'metadata': '3.1.1'}, 'PLATFORM': 'linux/amd64', 'CI': 'true'}
+rootdir: /mnt/data/banking_pytest_session9
+configfile: pytest.ini
+testpaths: tests
+plugins: anyio-4.13.0, ddtrace-4.4.0, Faker-40.1.2, asyncio-1.3.0, cov-7.0.0, json-report-1.5.0, metadata-3.1.1
+asyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=None, asyncio_default_test_loop_scope=function
+collecting ... collected 17 items
+
+tests/test_banking.py::test_deposit_bva[1-100001] PASSED                 [  5%]
+tests/test_banking.py::test_deposit_bva[99999-199999] PASSED             [ 11%]
+tests/test_banking.py::test_deposit_bva[100000-200000] PASSED            [ 17%]
+tests/test_banking.py::test_deposit_bva[100001-200001] PASSED            [ 23%]
+tests/test_banking.py::test_deposit_zero_raises PASSED                   [ 29%]
+tests/test_banking.py::test_deposit_negative_raises PASSED               [ 35%]
+tests/test_banking.py::test_withdraw_valid_boundaries[1-99999] PASSED    [ 41%]
+tests/test_banking.py::test_withdraw_valid_boundaries[99999-1] PASSED    [ 47%]
+tests/test_banking.py::test_withdraw_valid_boundaries[100000-0] PASSED   [ 52%]
+tests/test_banking.py::test_withdraw_zero_raises PASSED                  [ 58%]
+tests/test_banking.py::test_withdraw_over_balance_raises PASSED          [ 64%]
+tests/test_banking.py::test_transfer_and_notification_mock PASSED        [ 70%]
+tests/test_banking.py::test_transfer_insufficient_funds_does_not_notify PASSED [ 76%]
+tests/test_banking.py::test_transfer_zero_raises PASSED                  [ 82%]
+tests/test_banking.py::test_transfer_to_self_raises PASSED               [ 88%]
+tests/test_banking.py::test_blank_owner_raises PASSED                    [ 94%]
+tests/test_banking.py::test_negative_initial_balance_raises PASSED       [100%]
+
+================================ tests coverage ================================
+_______________ coverage: platform linux, python 3.13.5-final-0 ________________
+
+Name         Stmts   Miss Branch BrPart  Cover   Missing
+--------------------------------------------------------
+banking.py      32      0     16      0   100%
+--------------------------------------------------------
+TOTAL           32      0     16      0   100%
+Coverage HTML written to dir htmlcov
+============================== 17 passed in 0.13s ==============================

notification_service.py

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+def send_notification(recipient, message):
+    """Placeholder for an external notification service."""
+    raise RuntimeError("External notification service is not configured")

pytest.ini

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+[pytest]
+testpaths = tests
+addopts = -v

requirements.txt

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+pytest>=8,<10
+pytest-cov>=5,<8

tests/conftest.py

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+import pytest
+from banking import BankAccount
+
+
+@pytest.fixture
+def account():
+    instance = BankAccount("Alice", 100_000)
+    yield instance
+    instance.balance = 0

tests/test_banking.py

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+from unittest.mock import patch
+import pytest
+from banking import BankAccount
+
+
+@pytest.mark.parametrize("amount, expected", [
+    (1, 100_001),
+    (99_999, 199_999),
+    (100_000, 200_000),
+    (100_001, 200_001),
+])
+def test_deposit_bva(account, amount, expected):
+    assert account.deposit(amount) == expected
+
+
+def test_deposit_zero_raises(account):
+    with pytest.raises(ValueError, match="Deposit must be positive"):
+        account.deposit(0)
+
+
+def test_deposit_negative_raises(account):
+    with pytest.raises(ValueError, match="Deposit must be positive"):
+        account.deposit(-1)
+
+
+@pytest.mark.parametrize("amount, expected", [
+    (1, 99_999),
+    (99_999, 1),
+    (100_000, 0),
+])
+def test_withdraw_valid_boundaries(account, amount, expected):
+    assert account.withdraw(amount) == expected
+
+
+def test_withdraw_zero_raises(account):
+    with pytest.raises(ValueError, match="Withdrawal must be positive"):
+        account.withdraw(0)
+
+
+def test_withdraw_over_balance_raises(account):
+    with pytest.raises(ValueError, match="Insufficient funds"):
+        account.withdraw(100_001)
+    assert account.balance == 100_000
+
+
+def test_transfer_and_notification_mock(account):
+    recipient = BankAccount("Bob", 10_000)
+    with patch("banking.send_notification") as mocked:
+        assert account.transfer(recipient, 40_000) == 60_000
+        assert recipient.balance == 50_000
+        mocked.assert_called_once_with("Bob", "Received 40000 from Alice")
+
+
+def test_transfer_insufficient_funds_does_not_notify(account):
+    recipient = BankAccount("Bob")
+    with patch("banking.send_notification") as mocked:
+        with pytest.raises(ValueError, match="Insufficient funds"):
+            account.transfer(recipient, 100_001)
+        mocked.assert_not_called()
+        assert account.balance == 100_000
+        assert recipient.balance == 0
+
+
+def test_transfer_zero_raises(account):
+    with pytest.raises(ValueError, match="Transfer must be positive"):
+        account.transfer(BankAccount("Bob"), 0)
+
+
+def test_transfer_to_self_raises(account):
+    with pytest.raises(ValueError, match="Cannot transfer to the same account"):
+        account.transfer(account, 100)
+
+
+def test_blank_owner_raises():
+    with pytest.raises(ValueError, match="Owner is required"):
+        BankAccount("  ")
+
+
+def test_negative_initial_balance_raises():
+    with pytest.raises(ValueError, match="Initial balance cannot be negative"):
+        BankAccount("Alice", -1)