diff --git a/DGM_outer.py b/DGM_outer.py
index 2c87f4bd..6713ac3b 100644
--- a/DGM_outer.py
+++ b/DGM_outer.py
@@ -100,7 +100,7 @@ def choose_selfimproves(output_dir, archive, selfimprove_size, method='random',
         parent_commits = random.choices(commits, probabilities, k=selfimprove_size)
     elif method == 'best':
         # Choose parents with the best score
-        sorted_commits = sorted(candidates, key=lambda x: candidates[x]['accuracy_score'])
+        sorted_commits = sorted(candidates, key=lambda x: candidates[x]['accuracy_score'], reverse=True)
         parent_commits = sorted_commits[:min(selfimprove_size, len(sorted_commits))]
         if len(parent_commits) < selfimprove_size:
             parent_commits.extend(random.choices(parent_commits, k=selfimprove_size - len(parent_commits)))
@@ -225,7 +225,7 @@ def main():
     parser.add_argument("--selfimprove_workers", type=int, default=2, help="Number of parallel workers for self-improvement attempts.")
     parser.add_argument(
         "--choose_selfimproves_method", type=str, default='score_child_prop',
-        choices=['random', 'score_prop', 'score_child_prop' 'best'],
+        choices=['random', 'score_prop', 'score_child_prop', 'best'],
         help="Method to choose self-improve attempts.",
     )
     parser.add_argument("--continue_from", type=str, default=None, help="Directory to continue the run from.")
diff --git a/test_dgm_outer.py b/test_dgm_outer.py
new file mode 100644
index 00000000..fdb6eb2d
--- /dev/null
+++ b/test_dgm_outer.py
@@ -0,0 +1,126 @@
+import argparse
+import importlib
+import json
+import sys
+import types
+from unittest import mock
+
+import pytest
+
+
+# DGM_outer imports runtime-only Docker helpers that are not needed for these
+# unit tests. Stub those modules so the selection and CLI logic stay isolated.
+self_improve_step = types.ModuleType('self_improve_step')
+self_improve_step.self_improve = mock.Mock()
+
+docker_utils = types.ModuleType('utils.docker_utils')
+docker_utils.setup_logger = mock.Mock()
+
+with mock.patch.dict(
+    sys.modules,
+    {
+        'self_improve_step': self_improve_step,
+        'utils.docker_utils': docker_utils,
+    },
+):
+    DGM_outer = importlib.import_module('DGM_outer')
+
+
+SCORES = {
+    'initial': 0.2,
+    'medium-score': 0.5,
+    'high-score': 0.9,
+}
+
+
+class ParsedArguments(Exception):
+    pass
+
+
+def write_candidate_metadata(output_dir):
+    for commit, score in SCORES.items():
+        commit_dir = output_dir / commit
+        commit_dir.mkdir()
+        metadata = {
+            'overall_performance': {
+                'accuracy_score': score,
+                'total_unresolved_ids': [f'{commit}-task'],
+                'total_emptypatch_ids': [],
+                'total_resolved_ids': [],
+            },
+        }
+        if commit != 'initial':
+            metadata['parent_commit'] = 'initial'
+        (commit_dir / 'metadata.json').write_text(json.dumps(metadata))
+
+
+def select_best_parents(tmp_path, selfimprove_size):
+    write_candidate_metadata(tmp_path)
+    entries = DGM_outer.choose_selfimproves(
+        tmp_path,
+        list(SCORES),
+        selfimprove_size,
+        method='best',
+        polyglot=True,
+    )
+    return [parent_commit for parent_commit, _ in entries]
+
+
+@pytest.mark.parametrize(
+    ('selfimprove_size', 'expected_parents'),
+    [
+        (1, ['high-score']),
+        (2, ['high-score', 'medium-score']),
+    ],
+)
+def test_choose_selfimproves_best_selects_highest_scores_first(
+    tmp_path, selfimprove_size, expected_parents
+):
+    assert select_best_parents(tmp_path, selfimprove_size) == expected_parents
+
+
+def test_choose_selfimproves_best_handles_size_larger_than_candidates(tmp_path):
+    selected_parents = select_best_parents(tmp_path, len(SCORES) + 1)
+
+    assert selected_parents[:len(SCORES)] == [
+        'high-score',
+        'medium-score',
+        'initial',
+    ]
+    assert set(selected_parents) == set(SCORES)
+
+
+def parse_main_args(monkeypatch, argv):
+    original_parse_args = argparse.ArgumentParser.parse_args
+
+    def parse_args(parser):
+        raise ParsedArguments(original_parse_args(parser, argv))
+
+    monkeypatch.setattr(argparse.ArgumentParser, 'parse_args', parse_args)
+    with pytest.raises(ParsedArguments) as parsed:
+        DGM_outer.main()
+    return parsed.value.args[0]
+
+
+@pytest.mark.parametrize('method', ['best', 'score_child_prop'])
+def test_cli_accepts_parent_selection_method(monkeypatch, method):
+    args = parse_main_args(
+        monkeypatch,
+        ['--choose_selfimproves_method', method],
+    )
+
+    assert args.choose_selfimproves_method == method
+
+
+def test_cli_rejects_concatenated_parent_selection_method(monkeypatch):
+    original_parse_args = argparse.ArgumentParser.parse_args
+
+    def parse_args(parser):
+        return original_parse_args(
+            parser,
+            ['--choose_selfimproves_method', 'score_child_propbest'],
+        )
+
+    monkeypatch.setattr(argparse.ArgumentParser, 'parse_args', parse_args)
+    with pytest.raises(SystemExit):
+        DGM_outer.main()