diff --git a/tests/test_system_init.py b/tests/test_system_init.py
new file mode 100644
index 0000000000..d321942d23
--- /dev/null
+++ b/tests/test_system_init.py
@@ -0,0 +1,90 @@
+from __future__ import annotations
+
+import unittest
+from unittest.mock import patch, MagicMock
+
+from src.system_init import build_system_init_message
+from src.setup import SetupReport, WorkspaceSetup
+
+
+class TestSystemInit(unittest.TestCase):
+    @patch("src.system_init.get_tools")
+    @patch("src.system_init.get_commands")
+    @patch("src.system_init.built_in_command_names")
+    @patch("src.system_init.run_setup")
+    def test_build_system_init_message_trusted(
+        self, mock_run_setup: MagicMock, mock_built_in: MagicMock, mock_get_commands: MagicMock, mock_get_tools: MagicMock
+    ) -> None:
+        # Setup mocks
+        mock_setup = MagicMock(spec=SetupReport)
+        mock_setup.trusted = True
+        mock_workspace = MagicMock(spec=WorkspaceSetup)
+        mock_workspace.startup_steps.return_value = ("step 1", "step 2")
+        mock_setup.setup = mock_workspace
+        mock_run_setup.return_value = mock_setup
+
+        mock_built_in.return_value = ["cmd1", "cmd2"]
+        mock_get_commands.return_value = [1, 2, 3, 4]  # Length 4
+        mock_get_tools.return_value = [1, 2, 3]  # Length 3
+
+        # Call the function
+        result = build_system_init_message(trusted=True)
+
+        # Assertions
+        mock_run_setup.assert_called_once_with(trusted=True)
+
+        expected_lines = [
+            "# System Init",
+            "",
+            "Trusted: True",
+            "Built-in command names: 2",
+            "Loaded command entries: 4",
+            "Loaded tool entries: 3",
+            "",
+            "Startup steps:",
+            "- step 1",
+            "- step 2",
+        ]
+        self.assertEqual(result, "\n".join(expected_lines))
+
+    @patch("src.system_init.get_tools")
+    @patch("src.system_init.get_commands")
+    @patch("src.system_init.built_in_command_names")
+    @patch("src.system_init.run_setup")
+    def test_build_system_init_message_untrusted(
+        self, mock_run_setup: MagicMock, mock_built_in: MagicMock, mock_get_commands: MagicMock, mock_get_tools: MagicMock
+    ) -> None:
+        # Setup mocks
+        mock_setup = MagicMock(spec=SetupReport)
+        mock_setup.trusted = False
+        mock_workspace = MagicMock(spec=WorkspaceSetup)
+        mock_workspace.startup_steps.return_value = ("only safe step",)
+        mock_setup.setup = mock_workspace
+        mock_run_setup.return_value = mock_setup
+
+        mock_built_in.return_value = []
+        mock_get_commands.return_value = []
+        mock_get_tools.return_value = []
+
+        # Call the function
+        result = build_system_init_message(trusted=False)
+
+        # Assertions
+        mock_run_setup.assert_called_once_with(trusted=False)
+
+        expected_lines = [
+            "# System Init",
+            "",
+            "Trusted: False",
+            "Built-in command names: 0",
+            "Loaded command entries: 0",
+            "Loaded tool entries: 0",
+            "",
+            "Startup steps:",
+            "- only safe step",
+        ]
+        self.assertEqual(result, "\n".join(expected_lines))
+
+
+if __name__ == "__main__":
+    unittest.main()