Add regression tests for get_latest and get_oldest functions

tests/test_utils_checkpointing.py

@@ -0,0 +1,36 @@
+"""
+Tests for functions in utils/checkpointing_utils.py
+"""
+
+import os
+import tempfile
+
+from fms_fsdp.utils.checkpointing_utils import get_latest, get_oldest
+
+
+def test_get_oldest():
+    """
+    Ensure that the get_oldest function returns the name of the file with the oldest
+    timestamp (i.e. that was created first).
+    """
+    with tempfile.TemporaryDirectory() as tempdir:
+        for i in range(3):
+            filename = os.path.join(tempdir, f"file_{i}")
+            print("random content", file=open(file=filename, mode="w"))
+
+        oldest_filename = get_oldest(targdir=tempdir)
+        assert oldest_filename.endswith("file_0")
+
+
+def test_get_latest():
+    """
+    Ensure that the get_latest function returns the name of the file with the latest
+    integer suffix (i.e. that was created last).
+    """
+    with tempfile.TemporaryDirectory() as tempdir:
+        for i in range(3):
+            filename = os.path.join(tempdir, f"file_{i}")
+            print("random content", file=open(file=filename, mode="w"))
+
+        latest_filename = get_latest(targdir=tempdir)
+        assert latest_filename.endswith("file_2")