tests: add a few more tests from pyproject-metadata

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

tests/test_metadata.py

@@ -1,4 +1,9 @@
+from __future__ import annotations
+
+import email.message
+import inspect
 import pathlib
+import textwrap
 
 import pytest
 
@@ -916,3 +921,166 @@ def test_modern_license(self):
         ]
 
         assert core_metadata.get_payload() is None
+
+    @pytest.mark.parametrize(
+        ("items", "data"),
+        [
+            pytest.param(
+                [],
+                "",
+                id="empty",
+            ),
+            pytest.param(
+                [
+                    ("Foo", "Bar"),
+                ],
+                "Foo: Bar\n",
+                id="simple",
+            ),
+            pytest.param(
+                [
+                    ("Foo", "Bar"),
+                    ("Foo2", "Bar2"),
+                ],
+                """\
+                Foo: Bar
+                Foo2: Bar2
+                """,
+                id="multiple",
+            ),
+            pytest.param(
+                [
+                    ("Foo", "Unicøde"),
+                ],
+                "Foo: Unicøde\n",
+                id="unicode",
+            ),
+            pytest.param(
+                [
+                    ("Foo", "🕵️"),
+                ],
+                "Foo: 🕵️\n",
+                id="emoji",
+            ),
+            pytest.param(
+                [
+                    ("Item", None),
+                ],
+                "",
+                id="none",
+            ),
+            pytest.param(
+                [
+                    ("ItemA", "ValueA"),
+                    ("ItemB", "ValueB"),
+                    ("ItemC", "ValueC"),
+                ],
+                """\
+                ItemA: ValueA
+                ItemB: ValueB
+                ItemC: ValueC
+                """,
+                id="order 1",
+            ),
+            pytest.param(
+                [
+                    ("ItemB", "ValueB"),
+                    ("ItemC", "ValueC"),
+                    ("ItemA", "ValueA"),
+                ],
+                """\
+                ItemB: ValueB
+                ItemC: ValueC
+                ItemA: ValueA
+                """,
+                id="order 2",
+            ),
+            pytest.param(
+                [
+                    ("ItemA", "ValueA1"),
+                    ("ItemB", "ValueB"),
+                    ("ItemC", "ValueC"),
+                    ("ItemA", "ValueA2"),
+                ],
+                """\
+                ItemA: ValueA1
+                ItemB: ValueB
+                ItemC: ValueC
+                ItemA: ValueA2
+                """,
+                id="multiple keys",
+            ),
+            pytest.param(
+                [
+                    ("ItemA", "ValueA"),
+                    ("ItemB", "ValueB1\nValueB2\nValueB3"),
+                    ("ItemC", "ValueC"),
+                ],
+                """\
+                ItemA: ValueA
+                ItemB: ValueB1
+                       ValueB2
+                       ValueB3
+                ItemC: ValueC
+                """,
+                id="multiline",
+            ),
+        ],
+    )
+    def test_headers(self, items: list[tuple[str, None | str]], data: str) -> None:
+        message = metadata.RFC822Message()
+
+        for name, value in items:
+            if value:
+                message[name] = value
+
+        data = textwrap.dedent(data) + "\n"
+        assert str(message) == data
+        assert bytes(message) == data.encode()
+
+        assert email.message_from_string(str(message)).items() == [
+            (a, "\n       ".join(b.splitlines())) for a, b in items if b is not None
+        ]
+
+    def test_body(self) -> None:
+        message = metadata.RFC822Message()
+
+        message["ItemA"] = "ValueA"
+        message["ItemB"] = "ValueB"
+        message["ItemC"] = "ValueC"
+        body = inspect.cleandoc(
+            """
+            Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris
+            congue semper fermentum. Nunc vitae tempor ante. Aenean aliquet
+            posuere lacus non faucibus.  In porttitor congue luctus. Vivamus eu
+            dignissim orci. Donec egestas mi ac ipsum volutpat, vel elementum
+            sapien consectetur. Praesent dictum finibus fringilla. Sed vel
+            feugiat leo. Nulla a pharetra augue, at tristique metus.
+
+            Aliquam fermentum elit at risus sagittis, vel pretium augue congue.
+            Donec leo risus, faucibus vel posuere efficitur, feugiat ut leo.
+            Aliquam vestibulum vel dolor id elementum. Ut bibendum nunc interdum
+            neque interdum, vel tincidunt lacus blandit. Ut volutpat
+            sollicitudin dapibus. Integer vitae lacinia ex, eget finibus nulla.
+            Donec sit amet ante in neque pulvinar faucibus sed nec justo.  Fusce
+            hendrerit massa libero, sit amet pulvinar magna tempor quis. ø
+            """
+        )
+        headers = inspect.cleandoc(
+            """
+            ItemA: ValueA
+            ItemB: ValueB
+            ItemC: ValueC
+            """
+        )
+        full = f"{headers}\n\n{body}"
+
+        message.set_payload(textwrap.dedent(body))
+
+        assert str(message) == full
+
+        new_message = email.message_from_string(str(message))
+        assert new_message.items() == message.items()
+        assert new_message.get_payload() == message.get_payload()
+
+        assert bytes(message) == full.encode("utf-8")