Write settings.yml parameters in original order (#2352)

Co-authored-by: Eneko Martin <[email protected]>

esmvalcore/_task.py

@@ -422,7 +422,7 @@ def write_settings(self):
             settings_copy.pop(sett, None)
 
         filename = run_dir / 'settings.yml'
-        filename.write_text(yaml.safe_dump(settings_copy))
+        filename.write_text(yaml.safe_dump(settings_copy, sort_keys=False))
 
         # If running an NCL script:
         if Path(self.script).suffix.lower() == '.ncl':

tests/integration/test_task.py

@@ -6,6 +6,7 @@
 from multiprocessing.pool import ThreadPool
 
 import pytest
+import yaml
 
 import esmvalcore
 from esmvalcore._task import (
@@ -245,6 +246,23 @@ def test_py_diagnostic_task_constructor(tmp_path):
     assert task.output_dir == tmp_path / 'mydiag'
 
 
+def test_py_diagnostic_task_write_settings(tmp_path):
+    """Test DiagnosticTask writtes settings in the user's order."""
+    diag_script = tmp_path / 'diag_cow.py'
+    task = _get_single_diagnostic_task(tmp_path, diag_script)
+    my_arg_dict = {
+        'b': [1],
+        'a': 3.,
+        'c': False
+    }
+    task.settings.update(my_arg_dict)
+    settings = task.write_settings()
+    with open(settings, 'r') as stream:
+        settings_data = yaml.safe_load(stream)
+
+    assert list(settings_data) == ['run_dir', 'b', 'a', 'c']
+
+
 def test_diagnostic_diag_script_none(tmp_path):
     """Test case when diagnostic script doesn't exist."""
     diag_script = tmp_path / 'diag_cow.py'