First implementation

README.md

@@ -0,0 +1,3 @@
+Demonstration of the use of "conditional cleanups" in `pytest`, as explored further in [this blog post](https://blog.scubbo.org/posts/conditional-cleanups-in-pytest).
+
+Run `pytest`, and observe that the tempfile is cleaned up for the passing test, but persisted for the failing test.

lib/main.py

@@ -0,0 +1,5 @@
+import pathlib
+
+# Very simple method as placeholder for logic being tested.
+def write_content_to_file(content: str, path: pathlib.Path) -> None:
+    path.write_text(content)

tests/conftest.py

@@ -0,0 +1,45 @@
+import pytest
+
+from typing import Callable
+
+# https://stackoverflow.com/questions/69281822/how-to-only-run-a-pytest-fixture-cleanup-on-test-error-or-failure,
+# Though syntax appears to have changed
+# https://docs.pytest.org/en/latest/example/simple.html#making-test-result-information-available-in-fixtures
+@pytest.hookimpl(hookwrapper=True)
+def pytest_runtest_makereport(item, call):
+    # execute all other hooks to obtain the report object
+    outcome = yield
+
+    # TODO - we may care about more than just a binary result!
+    # (i.e. a skipped test is neither passed nor failed...probably?)
+    setattr(
+        item,
+        "rep_" + outcome.get_result().when + "_passed",
+        outcome.get_result().passed,
+    )
+
+
+class Cleanups(object):
+    def __init__(self):
+        self.success_cleanups = []
+        self.failure_cleanups = []
+
+    def add_success(self, success_cleanup: Callable[[], None]):
+        self.success_cleanups.append(success_cleanup)
+
+    def add_failure(self, failure_cleanup: Callable[[], None]):
+        self.failure_cleanups.append(failure_cleanup)
+
+
+@pytest.fixture
+def cleanups(request):
+    cleanups = Cleanups()
+    yield cleanups
+
+    if request.node.rep_call_passed:
+        cleanups = cleanups.success_cleanups
+    else:
+        cleanups = cleanups.failure_cleanups
+    if cleanups:
+        for cleanup in cleanups[::-1]:  # Apply in reverse order
+            cleanup()

tests/test_basic.py

@@ -0,0 +1,39 @@
+import os
+import tempfile
+import pytest
+
+import pathlib
+
+from lib.main import write_content_to_file
+
+
+@pytest.mark.parametrize("test_input", ["Expected content", "Incorrect content"])
+def test(test_input, temp_file_path, cleanups):
+
+    write_content_to_file(test_input, temp_file_path)
+
+    def in_test_print_out_on_test_failure():
+        print(f'(In-test cleanup) Test using tempfile {temp_file_path} failed')
+    cleanups.add_failure(in_test_print_out_on_test_failure)
+
+    assert temp_file_path.read_text() == "Expected content"
+
+    
+    
+@pytest.fixture
+def temp_file_path(cleanups) -> pathlib.Path:
+    # In real production use, you'd be more likely to use methods from the `tempfile` library
+    # (https://docs.python.org/3/library/tempfile.html) directly - but I'm implementing this fixture by-hand to
+    # demonstrate that the `cleanups` object can handle cleanup-methods being attached from within a fixture.
+    f = tempfile.NamedTemporaryFile(delete=False, dir='.')
+    path = pathlib.Path(f.name)
+
+    def delete_temp_file_on_test_success():
+        path.unlink()
+    cleanups.add_success(delete_temp_file_on_test_success)
+
+    def print_out_temp_file_path_on_test_failure():
+        print(f'Test failed involving tempfile {path}')
+    cleanups.add_failure(print_out_temp_file_path_on_test_failure)
+
+    return path