test: write basic tests of image comparsion with Pillow

tests/.gitignore

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+__errors__

tests/test_match_snapshot_images.py

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+import os
+from shutil import rmtree
+
+import pytest
+
+from match_snapshot import MatchSnapshot
+
+
+class Element:
+    def screenshot(self, path):
+        pass
+
+
+class TestsMatchSnapshotWithImages(MatchSnapshot):
+    def test_match_snapshot_same_images(self):
+        self.snapshot_path = "./tests/__snapshots__"
+        id = "python_home_page"
+
+        with open("./tests/__snapshots__/snapshot_python_home_page.png", "rb") as f1:
+            with open("./tests/__snapshots__/compare_python_home_page.png", "wb") as f2:
+                f2.write(f1.read())
+
+        self.assert_match_snapshot(Element(), id)
+
+    def test_match_snapshot_wrong_image(self):
+        self.snapshot_path = "./tests/__snapshots__"
+        self.failed_path = "./tests/__errors__"
+        id = "python_home_wrong_box"
+        if os.path.exists("./tests/__errors__"):
+            rmtree("./tests/__errors__")
+
+        with open("./tests/__snapshots__/snapshot_python_home_page.png", "rb") as f1:
+            with open(
+                "./tests/__snapshots__/compare_python_home_wrong_box.png", "wb"
+            ) as f2:
+                f2.write(f1.read())
+
+        with pytest.raises(AssertionError):
+            self.assert_match_snapshot(Element(), id)
+
+        assert os.path.exists(f"./tests/__errors__/{id}/comparison.png")
+        assert os.path.exists(f"./tests/__errors__/{id}/difference_threshold.png")
+        assert os.path.exists(f"./tests/__errors__/{id}/difference.png")
+        assert os.path.exists(f"./tests/__errors__/{id}/snapshot.png")
+        assert os.path.isfile(f"./tests/__errors__/{id}/comparison.png")
+        assert os.path.isfile(f"./tests/__errors__/{id}/difference_threshold.png")
+        assert os.path.isfile(f"./tests/__errors__/{id}/difference.png")
+        assert os.path.isfile(f"./tests/__errors__/{id}/snapshot.png")
+
+        if os.path.exists("./tests/__errors__"):
+            rmtree("./tests/__errors__")
+
+    def test_match_snapshot_threshold(self):
+        self.snapshot_path = "./tests/__snapshots__"
+        id = "python_home_threshold"
+
+        with open("./tests/__snapshots__/snapshot_python_home_page.png", "rb") as f1:
+            with open(
+                "./tests/__snapshots__/compare_python_home_threshold.png", "wb"
+            ) as f2:
+                f2.write(f1.read())
+
+        self.assert_match_snapshot(Element(), id)