trying to workout how to how to accurately determine mtime resolution

fileformats/core/fs_mount_identifier.py

@@ -171,20 +171,24 @@ def get_mtime_resolution(cls, path: PathLike) -> int:
             the root of the mount the path sits on
         fstype : str
             the type of the file-system (e.g. ext4 or cifs)"""
-        mount_point, _ = cls.get_mount(path)
-        # try:
-        #     resolution = cls.FS_MTIME_NS_RESOLUTION[fstype]
-        # except KeyError:
-        #     try:
-        resolution = cls.measure_mtime_resolution(mount_point)
-        # except (RuntimeError, OSError):
-        #     # Fallback to the largest known mtime
-        #     resolution = max(cls.FS_MTIME_NS_RESOLUTION.values())
+        mount_point, fstype = cls.get_mount(path)
+        try:
+            resolution = cls.FS_MTIME_NS_RESOLUTION[fstype]
+        except KeyError:
+            try:
+                resolution = cls.measure_mtime_resolution(path)
+            except (RuntimeError, OSError):
+                # Fallback to the largest known mtime
+                resolution = max(cls.FS_MTIME_NS_RESOLUTION.values())
+            else:
+                cls.FS_MTIME_NS_RESOLUTION[fstype] = resolution
         return resolution
 
     @classmethod
-    def measure_mtime_resolution(cls, mount_point: Path) -> int:
-        tmp_file = Path(mount_point) / ".__fileformats_mtime_measurement_test_file__"
+    def measure_mtime_resolution(cls, sample_path: PathLike) -> int:
+        tmp_file = (
+            Path(sample_path).parent / ".__fileformats_mtime_measurement_test_file__"
+        )
         tmp_file.touch()
         try:
             # Get the initial mtime
@@ -198,11 +202,15 @@ def measure_mtime_resolution(cls, mount_point: Path) -> int:
                     # Calculate the resolution
                     resolution = new_mtime - initial_mtime
                     return resolution
-            raise RuntimeError(f"Couldn't determine the mtime for the {mount_point}")
+            raise RuntimeError(
+                f"Couldn't determine the mtime for the file-system that {sample_path}"
+                "is stored on"
+            )
         finally:
             tmp_file.unlink()
 
     _mount_table: ty.Optional[ty.List[ty.Tuple[str, str]]] = None
+    # _inode_size_table: ty.Dict[str, int] = {}
 
     # Define a table of file system types and their mtime resolutions (in seconds)
     FS_MTIME_NS_RESOLUTION: ty.Dict[str, int] = {

fileformats/core/tests/test_decorators.py

@@ -1,4 +1,5 @@
 from pathlib import Path
+import time
 from fileformats.core.decorators import (
     mtime_cached_property,
     enough_time_has_elapsed_given_mtime_resolution,
@@ -20,6 +21,9 @@ def test_mtime_cached_property(tmp_path: Path):
     fspath.write_text("hello")
 
     file = MtimeTestFile(fspath)
+    time.sleep(
+        2
+    )  # ensure enough time has elapsed since file creation/modification for mtime to increment
 
     file.flag = 0
     assert file.cached_prop == 0
@@ -31,7 +35,7 @@ def test_mtime_cached_property(tmp_path: Path):
 
 def test_enough_time_has_elapsed_given_mtime_resolution():
     assert enough_time_has_elapsed_given_mtime_resolution(
-        [("", 110), ("", 220), ("", 300)], 311
+        [("", 110), ("", 220), ("", 300)], int(3e9)  # need to make it high for windows
     )