fix: clamp convert_size_bytes_to_string at largest unit (#184)

src/fsutil/converters.py

@@ -11,7 +11,7 @@ def convert_size_bytes_to_string(size: int) -> str:
     units = SIZE_UNITS
     factor = 0
     factor_limit = len(units) - 1
-    while (size_num >= 1024) and (factor <= factor_limit):
+    while (size_num >= 1024) and (factor < factor_limit):
         size_num /= 1024
         factor += 1
     size_units = units[factor]

tests/test_converters.py

@@ -19,6 +19,21 @@ def test_convert_size_bytes_to_string(size_bytes, expected_output):
     assert fsutil.convert_size_bytes_to_string(size_bytes) == expected_output
 
 
+@pytest.mark.parametrize(
+    "size_bytes, expected_output",
+    [
+        (2**80, "1.00 YB"),
+        (2**90, "1024.00 YB"),
+        (2**100, "1048576.00 YB"),
+    ],
+)
+def test_convert_size_bytes_to_string_saturates_at_largest_unit(
+    size_bytes, expected_output
+):
+    # Sizes at or above 1024 YB must clamp to the YB unit, not raise IndexError.
+    assert fsutil.convert_size_bytes_to_string(size_bytes) == expected_output
+
+
 @pytest.mark.parametrize(
     "size_string, expected_output",
     [