diff --git a/commitloom/services/metrics.py b/commitloom/services/metrics.py
index 75413ae..41e5e44 100644
--- a/commitloom/services/metrics.py
+++ b/commitloom/services/metrics.py
@@ -122,6 +122,9 @@ def _save_metrics(self, metrics: CommitMetrics) -> None:
             try:
                 with open(self._metrics_file) as f:
                     metrics_list = json.load(f)
+                if not isinstance(metrics_list, list):
+                    logger.warning("Invalid metrics file format, creating new file")
+                    metrics_list = []
             except (json.JSONDecodeError, FileNotFoundError) as e:
                 logger.warning(f"Failed to load metrics, creating new file: {str(e)}")
                 metrics_list = []
diff --git a/tests/test_metrics.py b/tests/test_metrics.py
new file mode 100644
index 0000000..f217750
--- /dev/null
+++ b/tests/test_metrics.py
@@ -0,0 +1,47 @@
+import json
+from datetime import timedelta
+
+from commitloom.services.metrics import metrics_manager, CommitMetrics
+
+
+def test_save_metrics_with_invalid_file(tmp_path, monkeypatch):
+    metrics_file = tmp_path / "metrics.json"
+    metrics_file.write_text("{}")  # invalid structure (dict instead of list)
+    monkeypatch.setattr(metrics_manager, "_metrics_file", metrics_file)
+
+    metric = CommitMetrics(files_changed=1)
+    # Should not raise even though existing file is invalid
+    metrics_manager._save_metrics(metric)
+
+    data = json.loads(metrics_file.read_text())
+    assert isinstance(data, list)
+    assert data[0]["files_changed"] == 1
+
+
+def test_format_timedelta_outputs():
+    td = timedelta(days=1, hours=2, minutes=30)
+    result = metrics_manager._format_timedelta(td)
+    assert "1 day" in result
+    assert "2 hours" in result
+    assert "30 minutes" in result
+
+
+def test_get_statistics(tmp_path, monkeypatch):
+    metrics_file = tmp_path / "metrics.json"
+    stats_file = tmp_path / "stats.json"
+    monkeypatch.setattr(metrics_manager, "_metrics_file", metrics_file)
+    monkeypatch.setattr(metrics_manager, "_stats_file", stats_file)
+
+    metrics_manager.start_commit_tracking("repo")
+    metrics_manager.finish_commit_tracking(
+        files_changed=1,
+        tokens_used=10,
+        prompt_tokens=5,
+        completion_tokens=5,
+        cost_in_eur=0.01,
+        model_used="gpt-test",
+    )
+
+    stats = metrics_manager.get_statistics()
+    assert stats["total_commits"] >= 1
+