test_imagefile.py improvements

Tests/test_imagefile.py

@@ -215,19 +215,44 @@ class MockPyDecoder(ImageFile.PyDecoder):
 
 
 class MockPyEncoder(ImageFile.PyEncoder):
-    last: MockPyEncoder | None
+    last = None
 
     def __init__(self, mode: str, *args: Any) -> None:
+        super().__init__(mode, *args)
+        self._pushes_fd = False
+        self.cleanup_called = False
         MockPyEncoder.last = self
 
-        super().__init__(mode, *args)
-
     def encode(self, buffer):
+        # Simulate encoding
+        if buffer is None:
+            raise NotImplementedError
         return 1, 1, b""
 
     def cleanup(self) -> None:
         self.cleanup_called = True
 
+def test_encode_to_file() -> None:
+    encoder = MockPyEncoder("RGBA")
+
+    with pytest.raises(NotImplementedError):
+        encoder.encode_to_file(None, None)
+
+    encoder._pushes_fd = True
+    with pytest.raises(NotImplementedError):
+        encoder.encode_to_file(None, None)
+
+    buffer = BytesIO(b"\x00" * 10)
+    encoder._pushes_fd = False
+    encoder.encode = lambda buffer: (1, 1, b"")
+    try:
+        encoder.encode_to_file(buffer, None)
+    except NotImplementedError:
+        pass
+
+    encoder.encode = lambda buffer: (_ for _ in ()).throw(NotImplementedError)
+    with pytest.raises(NotImplementedError):
+        encoder.encode_to_file(buffer, None)
 
 xoff, yoff, xsize, ysize = 10, 20, 100, 100