fix: support call syntax for snapshot fixture overriding (#160)

* wip: call syntax with differentiation

* test: add example

* refactor: callout state mutation

* cr: restore fixture instance options after assertion

* cr: fix typo

Co-authored-by: Noah <noah.negin-ulster@tophatmonocle.com>

src/syrupy/assertion.py

@@ -43,6 +43,7 @@ class SnapshotAssertion:
     _extension_class: Type["AbstractSyrupyExtension"] = attr.ib(kw_only=True)
     _test_location: "TestLocation" = attr.ib(kw_only=True)
     _update_snapshots: bool = attr.ib(kw_only=True)
+    _extension: Optional["AbstractSyrupyExtension"] = attr.ib(init=False, default=None)
     _executions: int = attr.ib(init=False, default=0, kw_only=True)
     _execution_results: Dict[int, "AssertionResult"] = attr.ib(
         init=False, factory=dict, kw_only=True
@@ -51,12 +52,15 @@ class SnapshotAssertion:
     def __attrs_post_init__(self) -> None:
         self._session.register_request(self)
 
+    def __init_extension(
+        self, extension_class: Type["AbstractSyrupyExtension"]
+    ) -> "AbstractSyrupyExtension":
+        return extension_class(test_location=self._test_location)
+
     @property
     def extension(self) -> "AbstractSyrupyExtension":
-        if not getattr(self, "_extension", None):
-            self._extension: "AbstractSyrupyExtension" = self._extension_class(
-                test_location=self._test_location
-            )
+        if not self._extension:
+            self._extension = self.__init_extension(self._extension_class)
         return self._extension
 
     @property
@@ -70,6 +74,10 @@ def executions(self) -> Dict[int, AssertionResult]:
     def use_extension(
         self, extension_class: Optional[Type["AbstractSyrupyExtension"]] = None,
     ) -> "SnapshotAssertion":
+        """
+        Creates a new snapshot assertion fixture with the same options but using
+        specified extension class. This does not preserve assertion index or state.
+        """
         return self.__class__(
             update_snapshots=self._update_snapshots,
             test_location=self._test_location,
@@ -92,6 +100,16 @@ def get_assert_diff(self, data: "SerializableData") -> List[str]:
             diff.extend(self.extension.diff_lines(serialized_data, snapshot_data))
         return diff
 
+    def __call__(
+        self, *, extension_class: Optional[Type["AbstractSyrupyExtension"]]
+    ) -> "SnapshotAssertion":
+        """
+        Modifies assertion instance options
+        """
+        if extension_class:
+            self._extension = self.__init_extension(extension_class)
+        return self
+
     def __repr__(self) -> str:
         attrs_to_repr = ["name", "num_executions"]
         attrs_repr = ", ".join(f"{a}={repr(getattr(self, a))}" for a in attrs_to_repr)
@@ -131,6 +149,13 @@ def _assert(self, data: "SerializableData") -> bool:
                 updated=snapshot_updated,
             )
             self._executions += 1
+            self._post_assert()
+
+    def _post_assert(self) -> None:
+        """
+        Restores assertion instance options
+        """
+        self._extension = None
 
     def _recall_data(self, index: int) -> Optional["SerializableData"]:
         try:

tests/__snapshots__/test_extension_image.ambr

@@ -0,0 +1,3 @@
+# name: test_multiple_snapshot_extensions.1
+  '<?xml version="1.0" encoding="UTF-8"?><svg viewBox="0 0 50 50" xmlns="http://www.w3.org/2000/svg"><g><rect width="50" height="50" fill="#fff"/><g><g fill="#fff" stroke="#707070"><rect width="50" height="50" stroke="none"/><rect x="0" y="0" width="50" height="50" fill="none"/></g><text transform="translate(10 27)" fill="#707070" font-family="ConsolasForPowerline, Consolas for Powerline" font-size="8"><tspan x="0" y="0">50 x 50</tspan></text></g></g></svg>'
+---

tests/test_extension_image.py

@@ -8,40 +8,48 @@
 )
 
 
+actual_png = base64.b64decode(
+    b"iVBORw0KGgoAAAANSUhEUgAAADIAAAAyBAMAAADsEZWCAAAAG1BMVEXMzMy"
+    b"Wlpaqqqq3t7exsbGcnJy+vr6jo6PFxcUFpPI/AAAACXBIWXMAAA7EAAAOxA"
+    b"GVKw4bAAAAQUlEQVQ4jWNgGAWjgP6ASdncAEaiAhaGiACmFhCJLsMaIiDAE"
+    b"QEi0WXYEiMCOCJAJIY9KuYGTC0gknpuHwXDGwAA5fsIZw0iYWYAAAAASUVO"
+    b"RK5CYII="
+)
+actual_svg = (
+    '<?xml version="1.0" encoding="UTF-8"?>'
+    '<svg viewBox="0 0 50 50" xmlns="http://www.w3.org/2000/svg">'
+    '<g><rect width="50" height="50" fill="#fff"/>'
+    '<g><g fill="#fff" stroke="#707070">'
+    '<rect width="50" height="50" stroke="none"/>'
+    '<rect x="0" y="0" width="50" height="50" fill="none"/></g>'
+    '<text transform="translate(10 27)" fill="#707070" '
+    'font-family="ConsolasForPowerline, Consolas for Powerline" font-size="8">'
+    '<tspan x="0" y="0">50 x 50</tspan></text></g></g></svg>'
+)
+
+
 @pytest.fixture
 def snapshot_png(snapshot):
     return snapshot.use_extension(PNGImageSnapshotExtension)
 
 
-def test_image(snapshot_png, snapshot_svg):
-    actual_png = base64.b64decode(
-        b"iVBORw0KGgoAAAANSUhEUgAAADIAAAAyBAMAAADsEZWCAAAAG1BMVEXMzMy"
-        b"Wlpaqqqq3t7exsbGcnJy+vr6jo6PFxcUFpPI/AAAACXBIWXMAAA7EAAAOxA"
-        b"GVKw4bAAAAQUlEQVQ4jWNgGAWjgP6ASdncAEaiAhaGiACmFhCJLsMaIiDAE"
-        b"QEi0WXYEiMCOCJAJIY9KuYGTC0gknpuHwXDGwAA5fsIZw0iYWYAAAAASUVO"
-        b"RK5CYII="
-    )
+def test_image(snapshot_png):
     assert actual_png == snapshot_png
 
 
-@pytest.fixture
-def snapshot_svg(snapshot):
-    return snapshot.use_extension(SVGImageSnapshotExtension)
+def test_image_vector(snapshot):
+    """
+    Example of creating a previewable svg snapshot
+    """
+    assert snapshot(extension_class=SVGImageSnapshotExtension) == actual_svg
 
 
-def test_image_vector(snapshot_svg):
+def test_multiple_snapshot_extensions(snapshot):
     """
-    Example of creating a previewable svg snapshot
+    Example of switching extension classes on the fly.
+    These should be indexed in order of assertion.
     """
-    actual_svg = (
-        '<?xml version="1.0" encoding="UTF-8"?>'
-        '<svg viewBox="0 0 50 50" xmlns="http://www.w3.org/2000/svg">'
-        '<g><rect width="50" height="50" fill="#fff"/>'
-        '<g><g fill="#fff" stroke="#707070">'
-        '<rect width="50" height="50" stroke="none"/>'
-        '<rect x="0" y="0" width="50" height="50" fill="none"/></g>'
-        '<text transform="translate(10 27)" fill="#707070" '
-        'font-family="ConsolasForPowerline, Consolas for Powerline" font-size="8">'
-        '<tspan x="0" y="0">50 x 50</tspan></text></g></g></svg>'
-    )
-    assert snapshot_svg == actual_svg
+    assert actual_svg == snapshot(extension_class=SVGImageSnapshotExtension)
+    assert actual_svg == snapshot  # uses initial extension class
+    assert actual_png == snapshot(extension_class=PNGImageSnapshotExtension)
+    assert actual_svg == snapshot(extension_class=SVGImageSnapshotExtension)