Add tests for saving to stdout

Tests/test_file_jpeg.py

@@ -1,5 +1,6 @@
 import os
 import re
+import sys
 from io import BytesIO
 
 import pytest
@@ -870,6 +871,33 @@ class TestFileJpeg:
             with Image.open("Tests/images/hopper.jpg") as im:
                 assert im.getxmp() == {}
 
+    @pytest.mark.parametrize("buffer", (True, False))
+    def test_save_stdout(self, buffer):
+        old_stdout = sys.stdout
+
+        if buffer:
+
+            class MyStdOut:
+                buffer = BytesIO()
+
+            mystdout = MyStdOut()
+        else:
+            mystdout = BytesIO()
+
+        sys.stdout = mystdout
+
+        with Image.open(TEST_FILE) as im:
+            im.save(sys.stdout, "JPEG")
+            im_roundtrip = self.roundtrip(im)
+
+        # Reset stdout
+        sys.stdout = old_stdout
+
+        if buffer:
+            mystdout = mystdout.buffer
+        reloaded = Image.open(mystdout)
+        assert_image_equal(reloaded, im_roundtrip)
+
 
 @pytest.mark.skipif(not is_win32(), reason="Windows only")
 @skip_unless_feature("jpg")

Tests/test_file_ppm.py

@@ -1,3 +1,6 @@
+import sys
+from io import BytesIO
+
 import pytest
 
 from PIL import Image
@@ -80,3 +83,30 @@ def test_mimetypes(tmp_path):
         f.write("PyCMYK\n128 128\n255")
     with Image.open(path) as im:
         assert im.get_format_mimetype() == "image/x-portable-anymap"
+
+
+@pytest.mark.parametrize("buffer", (True, False))
+def test_save_stdout(buffer):
+    old_stdout = sys.stdout
+
+    if buffer:
+
+        class MyStdOut:
+            buffer = BytesIO()
+
+        mystdout = MyStdOut()
+    else:
+        mystdout = BytesIO()
+
+    sys.stdout = mystdout
+
+    with Image.open(TEST_FILE) as im:
+        im.save(sys.stdout, "PPM")
+
+    # Reset stdout
+    sys.stdout = old_stdout
+
+    if buffer:
+        mystdout = mystdout.buffer
+    reloaded = Image.open(mystdout)
+    assert_image_equal_tofile(reloaded, TEST_FILE)