DEVX-20: feat: extract Docker daemon start to tested Python module

tests/unit/test_start_docker.py

@@ -0,0 +1,98 @@
+"""Unit tests for devx.molecule.start_docker."""
+
+from unittest.mock import MagicMock, mock_open, patch
+
+from click.testing import CliRunner
+
+from devx.molecule.start_docker import is_docker_ready, main, start_docker_daemon
+
+
+class TestIsDockerReady:
+    @patch("devx.molecule.start_docker.subprocess.run")
+    def test_ready(self, mock_run: MagicMock) -> None:
+        mock_run.return_value = MagicMock(returncode=0)
+        assert is_docker_ready() is True
+        mock_run.assert_called_once_with(["docker", "info"], capture_output=True, check=False)
+
+    @patch("devx.molecule.start_docker.subprocess.run")
+    def test_not_ready(self, mock_run: MagicMock) -> None:
+        mock_run.return_value = MagicMock(returncode=1)
+        assert is_docker_ready() is False
+
+
+class TestStartDockerDaemon:
+    @patch("devx.molecule.start_docker.is_docker_ready", return_value=True)
+    def test_already_running(self, mock_ready: MagicMock) -> None:
+        assert start_docker_daemon() is True
+        mock_ready.assert_called_once()
+
+    @patch("devx.molecule.start_docker.time.sleep")
+    @patch("devx.molecule.start_docker.is_docker_ready")
+    @patch("devx.molecule.start_docker.subprocess.Popen")
+    @patch("builtins.open", new_callable=mock_open)
+    def test_starts_successfully(
+        self,
+        mock_file: MagicMock,
+        mock_popen: MagicMock,
+        mock_ready: MagicMock,
+        mock_sleep: MagicMock,
+    ) -> None:
+        # First call: initial check (not ready). Second: first loop iteration (ready).
+        mock_ready.side_effect = [False, True]
+        assert start_docker_daemon(timeout=5) is True
+        mock_popen.assert_called_once()
+        mock_sleep.assert_not_called()
+
+    @patch("devx.molecule.start_docker.time.sleep")
+    @patch("devx.molecule.start_docker.is_docker_ready", return_value=False)
+    @patch("devx.molecule.start_docker.subprocess.Popen")
+    @patch("builtins.open", new_callable=mock_open)
+    def test_fails_after_timeout(
+        self,
+        mock_file: MagicMock,
+        mock_popen: MagicMock,
+        mock_ready: MagicMock,
+        mock_sleep: MagicMock,
+    ) -> None:
+        # is_docker_ready always returns False: 1 initial + 3 loop iterations = 4 calls
+        assert start_docker_daemon(timeout=3) is False
+        mock_popen.assert_called_once()
+        assert mock_sleep.call_count == 3
+
+    @patch("devx.molecule.start_docker.time.sleep")
+    @patch("devx.molecule.start_docker.is_docker_ready")
+    @patch("devx.molecule.start_docker.subprocess.Popen")
+    @patch("builtins.open", new_callable=mock_open)
+    def test_custom_timeout(
+        self,
+        mock_file: MagicMock,
+        mock_popen: MagicMock,
+        mock_ready: MagicMock,
+        mock_sleep: MagicMock,
+    ) -> None:
+        # First call: initial check (not ready). Then 9 loop iterations (not ready),
+        # 10th iteration (ready).
+        mock_ready.side_effect = [False] * 10 + [True]
+        assert start_docker_daemon(timeout=10) is True
+        assert mock_sleep.call_count == 9
+
+
+class TestMain:
+    @patch("devx.molecule.start_docker.start_docker_daemon", return_value=True)
+    def test_success(self, mock_start: MagicMock) -> None:
+        runner = CliRunner()
+        result = runner.invoke(main, [])
+        assert result.exit_code == 0
+
+    @patch("devx.molecule.start_docker.start_docker_daemon", return_value=False)
+    def test_failure(self, mock_start: MagicMock) -> None:
+        runner = CliRunner()
+        result = runner.invoke(main, [])
+        assert result.exit_code == 1
+
+    @patch("devx.molecule.start_docker.start_docker_daemon", return_value=True)
+    def test_custom_timeout_flag(self, mock_start: MagicMock) -> None:
+        runner = CliRunner()
+        result = runner.invoke(main, ["--timeout", "60"])
+        assert result.exit_code == 0
+        mock_start.assert_called_once_with(60)