test: snapshot tests (#495)

Closes #482
Closes #483

### Summary of Changes

* Use [sypury](https://github.com/tophat/syrupy) snapshot tests for
images. Run `pytest --snapshot-update` to update snapshots after
changes.
* Fix random test failures due to TCL when running tests in a terminal

---------

Co-authored-by: megalinter-bot <129584137+megalinter-bot@users.noreply.github.com>

pyproject.toml

@@ -27,6 +27,7 @@ seaborn = "^0.13.0"
 [tool.poetry.group.dev.dependencies]
 pytest = "^7.2.1"
 pytest-cov = "^4.0.0"
+syrupy = "^4.6.0"
 
 [tool.poetry.group.docs.dependencies]
 jupyter = "^1.0.0"

tests/conftest.py

@@ -0,0 +1,35 @@
+from typing import Any
+
+import matplotlib as mpl
+import pytest
+from safeds.data.image.containers import Image
+from syrupy import SnapshotAssertion
+from syrupy.extensions.single_file import SingleFileSnapshotExtension
+from syrupy.types import SerializedData
+
+# Fix for failures when running pytest in a terminal (https://github.com/Safe-DS/Library/issues/482)
+mpl.use("agg")
+
+
+class JPEGImageExtension(SingleFileSnapshotExtension):
+    _file_extension = "jpg"
+
+    def serialize(self, data: Image, **_kwargs: Any) -> SerializedData:
+        return data._repr_jpeg_()
+
+
+@pytest.fixture()
+def snapshot_jpeg(snapshot: SnapshotAssertion) -> SnapshotAssertion:
+    return snapshot.use_extension(JPEGImageExtension)
+
+
+class PNGImageSnapshotExtension(SingleFileSnapshotExtension):
+    _file_extension = "png"
+
+    def serialize(self, data: Image, **_kwargs: Any) -> SerializedData:
+        return data._repr_png_()
+
+
+@pytest.fixture()
+def snapshot_png(snapshot: SnapshotAssertion) -> SnapshotAssertion:
+    return snapshot.use_extension(PNGImageSnapshotExtension)