Avoid copying db files if not necessary

tests/tempdiskimage.py

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+""" Create a temporary disk image on MacOS """
+
+import pathlib
+import platform
+import subprocess
+import tempfile
+import time
+
+
+class TempDiskImage:
+    """ Create and mount a temporary disk image """
+
+    def __init__(self, size=100, prefix=None):
+        """ Create and mount a temporary disk image.
+        
+        Args:
+            size: int; size in MB of disk image, default = 100
+            prefix: str; optional prefix to prepend to name of the temporary disk image
+            name: str; name of the mounted volume, default = "TemporaryDiskImage"
+
+        Raises:
+            TypeError if size is not int
+            RunTimeError if not on MacOS
+        """
+        if type(size) != int:
+            raise TypeError("size must be int")
+
+        system = platform.system()
+        if system != "Darwin":
+            raise RuntimeError("TempDiskImage only runs on MacOS")
+
+        self._tempdir = tempfile.TemporaryDirectory()
+        # hacky mktemp: this could create a race condition but unlikely given it's created in a TemporaryDirectory
+        prefix = "TemporaryDiskImage" if prefix is None else prefix
+        volume_name = f"{prefix}_{str(time.time()).replace('.','_')}_{str(time.perf_counter()).replace('.','_')}"
+        image_name = f"{volume_name}.dmg"
+        image_path = pathlib.Path(self._tempdir.name) / image_name
+        hdiutil = subprocess.run(
+            [
+                "/usr/bin/hdiutil",
+                "create",
+                "-size",
+                f"{size}m",
+                "-fs",
+                "HFS+",
+                "-volname",
+                volume_name,
+                image_path,
+            ],
+            check=True,
+            text=True,
+            capture_output=True,
+        )
+
+        if "created" not in hdiutil.stdout:
+            raise OSError(f"Could not create DMG {image_path}")
+
+        self.path = image_path
+        self._mount_point, self.name = self._mount_image(self.path)
+
+    def _mount_image(self, image_path):
+        """ mount a DMG file and return path, returns (mount_point, path) """
+        hdiutil = subprocess.run(
+            ["/usr/bin/hdiutil", "attach", image_path],
+            check=True,
+            text=True,
+            capture_output=True,
+        )
+        mount_point, path = None, None
+        for line in hdiutil.stdout.split("\n"):
+            line = line.strip()
+            if "Apple_HFS" not in line:
+                continue
+            output = line.split()
+            if len(output) < 3:
+                raise ValueError(f"Error mounting disk image {image_path}")
+            mount_point = output[0]
+            path = output[2]
+            break
+        return (mount_point, path)
+
+    def unmount(self):
+        try:
+            if self._mount_point:
+                hdiutil = subprocess.run(
+                    ["/usr/bin/hdiutil", "detach", self._mount_point],
+                    check=True,
+                    text=True,
+                    capture_output=True,
+                )
+                self._mount_point = None
+        except AttributeError:
+            pass
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.unmount()
+        if exc_type:
+            return False
+
+
+if __name__ == "__main__":
+    # Create a temporary disk image, 50mb in size
+    img = TempDiskImage(size=50, prefix="MyDiskImage")
+    # Be sure to unmount it, image will be cleaned up automatically
+    img.unmount()
+
+    # Or use it as a context handler
+    # Default values are 100mb and prefix = "TemporaryDiskImage"
+    with TempDiskImage() as img:
+        print(f"image: {img.path}")
+        print(f"mounted at: {img.name}")