Fix a bug in "Change Selection"

Fix a bug in the "Change Selection" action, whereby changing your
selection and picking files from another directory results in:

    "Dangerzone does not support adding documents from multiple
    locations. The newly added documents were ignored."

To fix this, change the output directory when we change selection as
well.

dangerzone/gui/main_window.py

@@ -488,24 +488,20 @@ class ContentWidget(QtWidgets.QWidget):
             ).exec_()
             return
 
-        # Get previously selected documents
-        self.dangerzone.clear_documents()
-        self.documents_list.clear()
-
-        # Assumed all files in batch are in the same directory
-        first_doc = docs[0]
-        output_dir = os.path.dirname(first_doc.input_filename)
-        if not self.dangerzone.output_dir:
-            self.dangerzone.output_dir = output_dir
-        elif self.dangerzone.output_dir != output_dir:
+        # Ensure all files in batch are in the same directory
+        dirnames = {os.path.dirname(doc.input_filename) for doc in docs}
+        if len(dirnames) > 1:
             Alert(
                 self.dangerzone,
                 message="Dangerzone does not support adding documents from multiple locations.\n\n The newly added documents were ignored.",
                 has_cancel=False,
             ).exec_()
             return
-        else:
-            self.dangerzone.output_dir = output_dir
+
+        # Clear previously selected documents
+        self.dangerzone.clear_documents()
+        self.documents_list.clear()
+        self.dangerzone.output_dir = list(dirnames)[0]
 
         for doc in docs:
             self.dangerzone.add_document(doc)

tests/gui/test_main_window.py

@@ -1,3 +1,6 @@
+import os
+import pathlib
+import shutil
 import time
 import typing
 
@@ -335,6 +338,7 @@ def test_change_document_button(
     mocker: MockerFixture,
     sample_pdf: str,
     sample_doc: str,
+    tmp_path: pathlib.Path,
 ) -> None:
     # Setup first doc selection
     file_dialog_mock = mocker.MagicMock()
@@ -350,7 +354,9 @@ def test_change_document_button(
         file_dialog_mock.accept()
 
     # Setup doc change
-    file_dialog_mock.selectedFiles.return_value = (sample_doc,)
+    shutil.copy(sample_doc, tmp_path)
+    tmp_sample_doc = tmp_path / os.path.basename(sample_doc)
+    file_dialog_mock.selectedFiles.return_value = (tmp_sample_doc,)
 
     # When clicking on "select docs" button
     with qtbot.waitSignal(content_widget.documents_added):
@@ -370,4 +376,4 @@ def test_change_document_button(
         for doc in content_widget.dangerzone.get_unconverted_documents()
     ]
     assert len(docs) is 1
-    assert docs[0] == sample_doc
+    assert docs[0] == str(tmp_sample_doc)