test: add multiple new test cases and update python version

1. update .python-version from 3.11 to 3.13
2. add tests for IS_RUNNING and DIR_EXISTS conditions
3. add graph-related tests including string ref parsing, mermaid output, GraphComposer and compose function
4. add storage backend TTL tests for both MemoryBackend and JSONBackend
5. add new system task tests for clr, reset_icon_cache, setenv and which
6. add comprehensive task spec tests including soft dependencies, retry policy, context managers and task template
7. add executor edge case tests for various scenarios

tests/test_system.py

@@ -0,0 +1,178 @@
+"""Tests for tasks/system.py."""
+
+import os
+import subprocess
+
+import pytest
+
+from pyflowx.conditions import Constants
+from pyflowx.tasks.system import clr, reset_icon_cache, setenv, which
+
+
+def test_clr_creates_task_spec() -> None:
+    """clr() 应创建 TaskSpec。"""
+    spec = clr()
+    assert spec.name == "clear_screen"
+    assert spec.fn is not None
+
+
+def test_clr_executes_on_linux(monkeypatch: pytest.MonkeyPatch) -> None:
+    """clr() 在 Linux 上应执行 clear 命令。"""
+    monkeypatch.setattr(Constants, "IS_WINDOWS", False)
+    monkeypatch.setattr(Constants, "IS_LINUX", True)
+
+    # Mock subprocess.run
+    ran = []
+    monkeypatch.setattr(
+        subprocess,
+        "run",
+        lambda cmd, **kw: ran.append(cmd),
+    )
+
+    spec = clr()
+    spec.fn()
+    assert ran == [["clear"]]
+
+
+def test_clr_executes_on_windows(monkeypatch: pytest.MonkeyPatch) -> None:
+    """clr() 在 Windows 上应执行 cls 命令。"""
+    monkeypatch.setattr(Constants, "IS_WINDOWS", True)
+
+    # Mock subprocess.run
+    ran = []
+    monkeypatch.setattr(
+        subprocess,
+        "run",
+        lambda cmd, **kw: ran.append(cmd),
+    )
+
+    spec = clr()
+    spec.fn()
+    assert ran == [["cls"]]
+
+
+def test_reset_icon_cache_non_windows(monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]) -> None:
+    """reset_icon_cache() 在非 Windows 上应返回空列表并打印提示。"""
+    monkeypatch.setattr(Constants, "IS_WINDOWS", False)
+
+    specs = reset_icon_cache()
+    assert specs == []
+    captured = capsys.readouterr()
+    assert "仅在 Windows 上支持" in captured.out
+
+
+def test_reset_icon_cache_windows(monkeypatch: pytest.MonkeyPatch) -> None:
+    """reset_icon_cache() 在 Windows 上应返回任务列表。"""
+    monkeypatch.setattr(Constants, "IS_WINDOWS", True)
+    monkeypatch.setenv("LOCALAPPDATA", "C:\\Users\\test\\AppData\\Local")
+
+    specs = reset_icon_cache()
+    assert len(specs) == 4
+    assert specs[0].name == "kill_explorer"
+    assert specs[1].name == "delete_icon_cache"
+    assert specs[2].name == "delete_icon_cache_all"
+    assert specs[3].name == "restart_explorer"
+
+
+def test_setenv_creates_task_spec() -> None:
+    """setenv() 应创建 TaskSpec。"""
+    spec = setenv("TEST_VAR", "test_value")
+    assert spec.name == "setenv_test_var"
+    assert spec.verbose is True
+
+
+def test_setenv_sets_environment_variable(monkeypatch: pytest.MonkeyPatch) -> None:
+    """setenv() 应设置环境变量。"""
+    spec = setenv("TEST_VAR", "test_value")
+    spec.fn()
+    assert os.environ["TEST_VAR"] == "test_value"
+
+
+def test_setenv_default_not_overwrite(monkeypatch: pytest.MonkeyPatch) -> None:
+    """setenv(default=True) 不应覆盖已存在的环境变量。"""
+    os.environ["TEST_VAR_EXISTS"] = "original"
+    spec = setenv("TEST_VAR_EXISTS", "new_value", default=True)
+    spec.fn()
+    assert os.environ["TEST_VAR_EXISTS"] == "original"
+
+
+def test_setenv_default_sets_when_missing() -> None:
+    """setenv(default=True) 应在缺失时设置环境变量。"""
+    # Ensure variable does not exist
+    if "PYFLOWX_TEST_VAR_MISSING" in os.environ:
+        del os.environ["PYFLOWX_TEST_VAR_MISSING"]
+
+    spec = setenv("PYFLOWX_TEST_VAR_MISSING", "default_value", default=True)
+    spec.fn()
+    assert os.environ["PYFLOWX_TEST_VAR_MISSING"] == "default_value"
+
+    # Clean up after test
+    del os.environ["PYFLOWX_TEST_VAR_MISSING"]
+
+
+def test_which_creates_task_spec() -> None:
+    """which() 应创建 TaskSpec。"""
+    spec = which("python")
+    assert spec.name == "which_python"
+
+
+def test_which_linux_found(monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]) -> None:
+    """which() 在 Linux 上找到命令应打印路径。"""
+    monkeypatch.setattr(Constants, "IS_WINDOWS", False)
+
+    class MockResult:
+        returncode = 0
+        stdout = "/usr/bin/python\n"
+
+    monkeypatch.setattr(
+        subprocess,
+        "run",
+        lambda cmd, **kw: MockResult(),
+    )
+
+    spec = which("python")
+    spec.fn()
+    captured = capsys.readouterr()
+    assert "python ->" in captured.out
+    assert "/usr/bin/python" in captured.out
+
+
+def test_which_windows_found(monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]) -> None:
+    """which() 在 Windows 上找到命令应打印路径。"""
+    monkeypatch.setattr(Constants, "IS_WINDOWS", True)
+
+    class MockResult:
+        returncode = 0
+        stdout = "C:\\Python\\python.exe\nC:\\Python\\Scripts\\python.exe\n"
+
+    monkeypatch.setattr(
+        subprocess,
+        "run",
+        lambda cmd, **kw: MockResult(),
+    )
+
+    spec = which("python")
+    spec.fn()
+    captured = capsys.readouterr()
+    assert "python ->" in captured.out
+    assert "C:\\Python\\python.exe" in captured.out
+
+
+def test_which_not_found(monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]) -> None:
+    """which() 未找到命令应打印提示。"""
+    monkeypatch.setattr(Constants, "IS_WINDOWS", False)
+
+    class MockResult:
+        returncode = 1
+        stdout = ""
+
+    monkeypatch.setattr(
+        subprocess,
+        "run",
+        lambda cmd, **kw: MockResult(),
+    )
+
+    spec = which("nonexistent_cmd")
+    spec.fn()
+    captured = capsys.readouterr()
+    assert "nonexistent_cmd -> 未找到" in captured.out