Fix so that fusion can be run more than once

Author: m-albert

src/napari_stitcher/_stitcher_widget.py

@@ -7,7 +7,7 @@
 Replace code below according to your needs.
 """
 from typing import TYPE_CHECKING
-import os, tempfile, sys
+import os, tempfile, sys, shutil
 from collections.abc import Iterable
 
 import numpy as np
@@ -389,6 +389,8 @@ def run_fusion(self):
             mfused = msi_utils.get_msim_from_sim(fused, scale_factors=[])
 
             tmp_fused_path = os.path.join(self.tmpdir.name, 'fused_%s.zarr' %ch)
+            if os.path.exists(tmp_fused_path):
+                shutil.rmtree(tmp_fused_path)
 
             with _utils.TemporarilyDisabledWidgets(self.all_widgets),\
                 _utils.VisibleActivityDock(self.viewer),\

src/napari_stitcher/_tests/test_stitcher_widget.py

@@ -221,6 +221,9 @@ def test_fusion_without_registration(make_napari_viewer):
     stitcher_widget.run_fusion()
     assert len(viewer.layers) == 3
 
+    #check that fusion can also be run twice
+    stitcher_widget.run_fusion()
+
 
 def test_vanilla_layers_2D_no_time(make_napari_viewer):