tests: Add a fixture for uncommon filenames

Add a pytest fixture that crafts a filename with Unicode characters that
are not considered common for this use. By default, this fixture uses
an invalid Unicode character as well, but we strip it in case of macOS
(APFS) since filenames must be UTF-8 encoded.

[1]: https://en.wikipedia.org/wiki/Filename#Comparison_of_filename_limitations

tests/__init__.py

@@ -1,3 +1,4 @@
+import platform
 import sys
 import zipfile
 from pathlib import Path
@@ -117,6 +118,22 @@ def uncommon_text() -> str:
     return "\033[31;1;4m BaD TeΧt \u200d ❌ \033[0m"
 
 
+@pytest.fixture
+def uncommon_filename(uncommon_text: str) -> str:
+    """Craft a filename with Unicode characters that are considered not common.
+
+    We reuse the same uncommon string as above, with a small exception for macOS.
+    Because the APFS filesystem in macOS accepts only UTF-8 encoded strings [1], we
+    cannot create a filename with invalid Unicode characters. So, in order to test the
+    rest of the corner cases, we replace U+DCF0 with an empty string.
+
+    [1]: https://en.wikipedia.org/wiki/Filename#Comparison_of_filename_limitations
+    """
+    if platform.system() == "Darwin":
+        uncommon_text = uncommon_text.replace("\udcf0", "")
+    return uncommon_text + ".pdf"
+
+
 @pytest.fixture
 def sanitized_text() -> str:
     """Return a sanitized version of the uncommon_text."""