Explicitly check for valid dates in FolderJournal and add unit test

tests/unit/test_journals_folder_journal.py

@@ -0,0 +1,60 @@
+# Copyright © 2012-2023 jrnl contributors
+# License: https://www.gnu.org/licenses/gpl-3.0.html
+
+import pathlib
+from unittest import mock
+
+import pytest
+
+import jrnl
+from jrnl.journals.FolderJournal import Folder
+
+
+@pytest.mark.parametrize(
+    "inputs_and_outputs",
+    [
+        [
+            "/2020/01",
+            ["02.txt", "03.txt", "31.txt"],
+            ["/2020/01/02.txt", "/2020/01/03.txt", "/2020/01/31.txt"],
+        ],
+        [
+            "/2020/02",  # leap year
+            ["02.txt", "03.txt", "28.txt", "29.txt", "31.txt", "39.txt"],
+            [
+                "/2020/02/02.txt",
+                "/2020/02/03.txt",
+                "/2020/02/28.txt",
+                "/2020/02/29.txt",
+            ],
+        ],
+        [
+            "/2100/02",  # not a leap year
+            ["01.txt", "28.txt", "29.txt", "39.txt"],
+            ["/2100/02/01.txt", "/2100/02/28.txt"],
+        ],
+        [
+            "/2023/04",
+            ["29.txt", "30.txt", "31.txt", "39.txt"],
+            ["/2023/04/29.txt", "/2023/04/30.txt"],
+        ],
+    ],
+)
+def test_get_day_files_expected_filtering(inputs_and_outputs):
+    year_month_path, glob_filenames, expected_output = inputs_and_outputs
+
+    year_month_path = pathlib.Path(year_month_path)
+
+    glob_files = map(lambda x: year_month_path / x, glob_filenames)
+    expected_output = list(map(lambda x: str(pathlib.PurePath(x)), expected_output))
+
+    with (
+        mock.patch("pathlib.Path.glob", return_value=glob_files),
+        mock.patch.object(pathlib.Path, "is_file", return_value=True),
+    ):
+        actual_output = list(Folder._get_day_files(year_month_path))
+        actual_output.sort()
+
+        expected_output.sort()
+
+        assert actual_output == expected_output