test: add test for cmd_save and cmd_load functionality

aider/commands.py

@@ -1246,7 +1246,6 @@ class Commands:
         output = f"{announcements}\n{settings}"
         self.io.tool_output(output)
 
-    # ai add cmd_save(fname) that generates a file that cmd_load can read!
     def cmd_load(self, args):
         "Load and execute commands from a file"
         if not args.strip():
@@ -1293,6 +1292,60 @@ class Commands:
         except Exception as e:
             self.io.tool_error(f"Error saving commands to file: {e}")
 
+
+    #ai move this to test_commands.py!
+    def test_cmd_save_and_load(self):
+        with GitTemporaryDirectory() as repo_dir:
+            io = InputOutput(pretty=False, fancy_input=False, yes=True)
+            coder = Coder.create(self.GPT35, None, io)
+            commands = Commands(io, coder)
+
+            # Create some test files
+            test_files = {
+                "file1.txt": "Content of file 1",
+                "file2.py": "print('Content of file 2')",
+                "subdir/file3.md": "# Content of file 3"
+            }
+
+            for file_path, content in test_files.items():
+                full_path = Path(repo_dir) / file_path
+                full_path.parent.mkdir(parents=True, exist_ok=True)
+                full_path.write_text(content)
+
+            # Add some files as editable and some as read-only
+            commands.cmd_add("file1.txt file2.py")
+            commands.cmd_read_only("subdir/file3.md")
+
+            # Save the session to a file
+            session_file = "test_session.txt"
+            commands.cmd_save(session_file)
+
+            # Verify the session file was created and contains the expected commands
+            self.assertTrue(Path(session_file).exists())
+            with open(session_file, encoding=io.encoding) as f:
+                commands_text = f.read()
+                self.assertIn("/add file1.txt", commands_text)
+                self.assertIn("/add file2.py", commands_text)
+                self.assertIn("/read-only subdir/file3.md", commands_text)
+
+            # Clear the current session
+            commands.cmd_reset("")
+            self.assertEqual(len(coder.abs_fnames), 0)
+            self.assertEqual(len(coder.abs_read_only_fnames), 0)
+
+            # Load the session back
+            commands.cmd_load(session_file)
+
+            # Verify files were restored correctly
+            added_files = {coder.get_rel_fname(f) for f in coder.abs_fnames}
+            read_only_files = {coder.get_rel_fname(f) for f in coder.abs_read_only_fnames}
+
+            self.assertEqual(added_files, {"file1.txt", "file2.py"})
+            self.assertEqual(read_only_files, {"subdir/file3.md"})
+
+            # Clean up
+            Path(session_file).unlink()
+
     def cmd_copy(self, args):
         "Copy the last assistant message to the clipboard"
         all_messages = self.coder.done_messages + self.coder.cur_messages