diff --git a/tests/unit/test_daily_digest.py b/tests/unit/test_daily_digest.py
new file mode 100644
index 00000000..7f19ab59
--- /dev/null
+++ b/tests/unit/test_daily_digest.py
@@ -0,0 +1,84 @@
+"""Tests for daily_digest.py"""
+
+import pytest
+from pathlib import Path
+from unittest.mock import patch
+from datetime import datetime
+
+from tradingagents.daily_digest import append_to_digest
+
+@pytest.fixture
+def mock_get_digest_path(tmp_path):
+    def _mock_path(date):
+        return tmp_path / "reports" / "daily" / date / "daily_digest.md"
+
+    with patch("tradingagents.daily_digest.get_digest_path", side_effect=_mock_path) as mock:
+        yield mock
+
+@pytest.fixture
+def mock_datetime():
+    class MockDatetime:
+        @classmethod
+        def now(cls):
+            return datetime(2023, 10, 26, 14, 30) # 14:30
+
+    with patch("tradingagents.daily_digest.datetime", MockDatetime):
+        yield MockDatetime
+
+def test_append_to_digest_new_file(mock_get_digest_path, mock_datetime, tmp_path):
+    date = "2023-10-26"
+    entry_type = "analyze"
+    label = "AAPL"
+    content = "Stock is going up."
+
+    result_path = append_to_digest(date, entry_type, label, content)
+
+    expected_path = tmp_path / "reports" / "daily" / date / "daily_digest.md"
+    assert result_path == expected_path
+    assert result_path.exists()
+
+    expected_content = (
+        f"# Daily Trading Report — {date}\n\n"
+        f"---\n### 14:30 — {label} ({entry_type})\n\n{content}\n\n"
+    )
+
+    assert result_path.read_text() == expected_content
+
+def test_append_to_digest_existing_file(mock_get_digest_path, mock_datetime, tmp_path):
+    date = "2023-10-26"
+
+    # First append (creates file)
+    append_to_digest(date, "analyze", "AAPL", "First content.")
+
+    # Change time for second append
+    with patch("tradingagents.daily_digest.datetime") as mock_dt:
+        mock_dt.now.return_value = datetime(2023, 10, 26, 15, 45) # 15:45
+
+        # Second append
+        result_path = append_to_digest(date, "scan", "Market Scan", "Second content.")
+
+    expected_path = tmp_path / "reports" / "daily" / date / "daily_digest.md"
+    assert result_path == expected_path
+
+    expected_content = (
+        f"# Daily Trading Report — {date}\n\n"
+        f"---\n### 14:30 — AAPL (analyze)\n\nFirst content.\n\n"
+        f"---\n### 15:45 — Market Scan (scan)\n\nSecond content.\n\n"
+    )
+
+    assert result_path.read_text() == expected_content
+
+def test_append_to_digest_existing_empty_file(mock_get_digest_path, mock_datetime, tmp_path):
+    date = "2023-10-26"
+    expected_path = tmp_path / "reports" / "daily" / date / "daily_digest.md"
+    expected_path.parent.mkdir(parents=True, exist_ok=True)
+    expected_path.write_text("") # Empty file
+
+    append_to_digest(date, "analyze", "AAPL", "Content")
+
+    # Should treat empty file like a non-existent file and add the header
+    expected_content = (
+        f"# Daily Trading Report — {date}\n\n"
+        f"---\n### 14:30 — AAPL (analyze)\n\nContent\n\n"
+    )
+    assert expected_path.read_text() == expected_content