additional notes on python testing

zk/Pytest_fixtures.md

@@ -0,0 +1,88 @@
+---
+tags: [python, pytest]
+---
+
+Fixtures are a way to provide data or state to your tests. Typically, although
+not exclusively, for processes that you want to reuse accross different `test_`
+functions. They are defined at the "arrange" stage of testing.
+
+## Example: testing class methods under test
+
+```py
+class Person:
+   def __init__(self, name):
+        self.name = name
+
+   def print_name(self):
+    return f"Your name is {self.name}"
+```
+
+To create a fixture of this class:
+
+```py
+@pytest.fixture
+def my_person():
+    person = new Person('Thomas')
+    return person.name()
+
+test_print_name(my_person):
+    assert(my_person) == 'Thomas'
+
+```
+
+> Note we define our fixture and then inject it into our test function.
+> Functions request fixtures they require by declaring them as arguments.
+
+Alternatively you could just return the class from the fixture and test the
+methods individually within the test function.
+
+## Integrating with `@patch` to provide mock fixtures
+
+Say we wanted to mock reading a JSON file.
+
+We could create a fixture:
+
+```py
+
+@pytest fixture
+def raw_json():
+    return json.dumps({"key": "value"})
+```
+
+And pass it in to the mock of the global `open` method:
+
+```py
+from unittest.mock import mock_open, patch
+
+def test_json_parsing(raw_json):
+    with patch("builtins.open", mock_open(read_data=raw_json))
+        # Then assert etc
+```
+
+This fixture could then be re-used to test any other method that relies on
+incoming JSON from a file.
+
+## Example: setup and teardown - before each and after each
+
+Fixtures can be leveraged to setup 'before each...' and 'after each...' logic:
+
+```py
+@pytest.fixture(scope="function")
+def setup():
+    os.environ["POCKET_LAMBDA_ENDPOINT"] = "https://some_endpoint.com/{article_type}"
+    yield
+    del os.environ["POCKET_LAMBDA_ENDPOINT"]
+```
+
+Here `yield` is a placeholder for the tests that run in between the setup and
+teardown.
+
+We use `scope="function"` to signal that this will run before/after any tests
+that inject the fixture.
+
+Then to specify the units that will run as the `yield` we just inject `setup`:
+
+```py
+def some_function(setup_function):
+    pass
+```

zk/Testing_Python_code.md

@@ -1,18 +1,16 @@
 ---
-tags: [python, testing]
+tags: [python, testing, pytest]
 ---
 
-# Testing Python code
-
 ## `pytest`
 
 Pytest is the most popular testing library for Python. It is not included with
 the Python standard library so it must be installed with
-[pip](Python_package_management.md).
+[pip](Python_package_management.md). While it does not include a declaration
-While it does not include a declaration library, it is robust enough to handle
+library, it is robust enough to handle most scenarios having a rich and
-most scenarios having a rich and expressive set of constructs and decorators
+expressive set of constructs and decorators that let you declare what your tests
-that let you declare what your tests should do, under what conditions they
+should do, under what conditions they should run, and how they should interact
-should run, and how they should interact with the rest of your system.
+with the rest of your system.
 
 ### Using `pytest`