feat(pytest): use v3 API in decoy fixture if annotated

Author: mcous

decoy/pytest_plugin.py

@@ -5,21 +5,32 @@
 but highly recommended.
 """
 
-from typing import Iterable
+from typing import TYPE_CHECKING, Iterable, Union, get_type_hints
 
 import pytest
 
 from decoy import Decoy
 
+if TYPE_CHECKING:
+    from decoy.next import Decoy as DecoyNext
+
 
 @pytest.fixture()
-def decoy() -> Iterable[Decoy]:
+def decoy(
+    request: pytest.FixtureRequest,
+) -> "Iterable[Union[Decoy, DecoyNext]]":
     """Get a [decoy.Decoy][] container and [reset it][decoy.Decoy.reset] after the test.
 
     This function is function-scoped [pytest fixture][] that will be
     automatically inserted by the plugin.
 
+    !!! tip
+
+        This fixture will automatically opt-into the [v3 preview API][v3-preview]
+        if annotated with `decoy.next.Decoy`.
+
     [pytest fixture]: https://docs.pytest.org/en/latest/how-to/fixtures.html
+    [v3-preview]: ./v3/about.md
 
     !!! example
         ```python
@@ -28,6 +39,20 @@ def test_my_thing(decoy: Decoy) -> None:
             # ...
         ```
     """
-    decoy = Decoy()
-    yield decoy
-    decoy.reset()
+    try:
+        decoy_hint = get_type_hints(request.function).get("decoy")
+        is_next = decoy_hint.__module__.startswith("decoy.next")
+
+    # purely defensive, probably won't ever raise
+    except Exception:  # pragma: no cover
+        is_next = False
+
+    if is_next:
+        from decoy.next import Decoy as DecoyNext
+
+        with DecoyNext.create() as decoy_next:
+            yield decoy_next
+    else:
+        decoy = Decoy()
+        yield decoy
+        decoy.reset()

docs/v3/about.md

@@ -28,14 +28,6 @@ Then, start trying out the new API!
 - from decoy import Decoy
 + from decoy.next import Decoy
 
-
-+ @pytest.fixture()
-+ def decoy() -> collections.abc.Iterator[Decoy]:
-+     """Create a Decoy v3 preview instance for testing."""
-+     with Decoy.create() as decoy:
-+         yield decoy
-
-
   def test_when(decoy: Decoy) -> None:
       mock = decoy.mock(cls=SomeClass)
 -     decoy.when(mock.foo("hello")).then_return("world")

docs/v3/migration.md

@@ -12,19 +12,16 @@ Recommended migration from v2:
 
 ## Setup
 
-For an incremental migration, you can set up a replacement `decoy` fixture wherever tests are being migrated:
+For an incremental migration, annotate a test's `decoy` fixture as `decoy.next.Decoy` to automatically opt-in that test to the preview API.
 
-```python
-import collections.abc
-import pytest
-
-from decoy.next import Decoy
+```diff
+- from decoy import Decoy
++ from decoy.next import Decoy
 
-@pytest.fixture()
-def decoy() -> collections.abc.Iterator[Decoy]:
-    """Create a Decoy instance for testing."""
-    with Decoy.create() as decoy:
-        yield decoy
+  def test_when(decoy: Decoy) -> None:
+      mock = decoy.mock(cls=SomeClass)
+-     decoy.when(mock.foo("hello")).then_return("world")
++     decoy.when(mock.foo).called_with("hello").then_return("world")
 ```
 
 ## When
@@ -189,6 +186,7 @@ In v3, `__enter__` and `__exit__` can still be stubbed to test advanced context
 
 ## Other breaking changes
 
+- The `mypy` plugin is no longer needed and will be removed
 - [`Decoy.mock`][decoy.next.Decoy.mock] is more strict about its arguments, and will raise [`MockSpecInvalidError`][decoy.errors.MockSpecInvalidError] if passed an invalid `spec` value.
 - [`IncorrectCallWarning`][decoy.warnings.IncorrectCallWarning] has been upgraded to an error: [`SignatureMismatchError`][decoy.errors.SignatureMismatchError].
 - Some "public" attributes have been removed from error classes.

pyproject.toml

@@ -77,11 +77,13 @@ test = "pytest -f"
 test-once = "coverage run --branch --source=decoy -m pytest --mypy-same-process"
 coverage = "coverage report"
 coverage-xml = "coverage xml"
+coverage-html = "coverage html"
 docs = "mkdocs serve --livereload"
 build-docs = "mkdocs build"
 build-package = "uv build"
 check-ci = ["check", "lint", "format-check"]
 test-ci = ["test-once", "coverage-xml"]
+test-coverage = ["test-once", "coverage-html", "coverage"]
 
 [tool.pytest.ini_options]
 addopts = "--color=yes --mypy-ini-file=tests/legacy/typing/mypy.ini --mypy-only-local-stub"

tests/test_matcher.py

@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-import collections.abc
 import dataclasses
 import sys
 from typing import Any, Callable, NamedTuple
@@ -33,13 +32,6 @@
 )
 
 
-@pytest.fixture()
-def decoy() -> collections.abc.Iterator[Decoy]:
-    """Create a Decoy instance for testing."""
-    with Decoy.create() as decoy:
-        yield decoy
-
-
 def test_matcher() -> None:
     """It matches based on a TypeIs function."""
 

tests/test_mock.py

@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-import collections.abc
 import inspect
 import sys
 from typing import Any
@@ -22,13 +21,6 @@
 )
 
 
-@pytest.fixture()
-def decoy() -> collections.abc.Iterator[Decoy]:
-    """Create a Decoy instance for testing."""
-    with Decoy.create() as decoy:
-        yield decoy
-
-
 def test_create_mock(decoy: Decoy) -> None:
     """It creates a callable mock that no-ops."""
     subject = decoy.mock(name="alice")

tests/test_pytest_plugin.py

@@ -1,11 +1,12 @@
 """Tests for Decoy's pytest plugin."""
 
+import sys
+
 import pytest
 
 
 def test_pytest_decoy_fixture(testdir: pytest.Testdir) -> None:
-    """It should add a decoy test fixture."""
-    # create a temporary pytest test file
+    """It adds a decoy test fixture."""
     testdir.makepyfile(
         """
         from decoy import Decoy
@@ -17,5 +18,60 @@ def test_decoy(decoy):
 
     result = testdir.runpytest_subprocess()
 
-    # check that all 4 tests passed
+    result.assert_outcomes(passed=1)
+
+
+@pytest.mark.skipif(sys.version_info < (3, 10), reason="v3 API required Python >= 3.10")
+def test_pytest_decoy_next_fixture(testdir: pytest.Testdir) -> None:
+    """It opts into the decoy.next API via annotation."""
+    testdir.makepyfile(
+        """
+        from decoy.next import Decoy
+
+        def test_decoy(decoy: Decoy):
+            assert isinstance(decoy, Decoy)
+        """
+    )
+
+    result = testdir.runpytest_subprocess()
+
+    result.assert_outcomes(passed=1)
+
+
+@pytest.mark.skipif(sys.version_info < (3, 10), reason="v3 API required Python >= 3.10")
+def test_pytest_decoy_next_fixture_fallback(testdir: pytest.Testdir) -> None:
+    """It falls back to v2 if annotations are messed up."""
+    testdir.makepyfile(
+        """
+        from decoy import Decoy
+
+        def test_decoy(decoy: 'Oops'):
+            assert isinstance(decoy, Decoy)
+        """
+    )
+
+    result = testdir.runpytest_subprocess()
+
+    result.assert_outcomes(passed=1)
+
+
+@pytest.mark.skipif(sys.version_info < (3, 10), reason="v3 API required Python >= 3.10")
+def test_pytest_decoy_next_fixture_nesting(testdir: pytest.Testdir) -> None:
+    """It opts into the decoy.next API via annotation for derived fixtures."""
+    testdir.makepyfile(
+        """
+        import pytest
+        from decoy.next import Decoy, Mock
+
+        @pytest.fixture()
+        def mock(decoy: Decoy):
+            return decoy.mock(name="mock")
+
+        def test_decoy(decoy: Decoy, mock: Mock):
+            assert isinstance(mock, Mock)
+        """
+    )
+
+    result = testdir.runpytest_subprocess()
+
     result.assert_outcomes(passed=1)

tests/test_verify.py

@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-import collections.abc
 import os
 import sys
 
@@ -22,13 +21,6 @@
 )
 
 
-@pytest.fixture()
-def decoy() -> collections.abc.Iterator[Decoy]:
-    """Create a Decoy instance for testing."""
-    with Decoy.create() as decoy:
-        yield decoy
-
-
 def test_verify(decoy: Decoy) -> None:
     """It no-ops if a call is verified."""
     subject = decoy.mock(name="subject")

tests/test_when.py

@@ -23,13 +23,6 @@
 )
 
 
-@pytest.fixture()
-def decoy() -> collections.abc.Iterator[Decoy]:
-    """Create a Decoy instance for testing."""
-    with Decoy.create() as decoy:
-        yield decoy
-
-
 def test_when_then_return(decoy: Decoy) -> None:
     """It returns a value."""
     subject = decoy.mock(name="subject")