diff --git a/.trae/rules/git-commit-message.md b/.trae/rules/git-commit-message.md
new file mode 100644
index 0000000..3eba4d4
--- /dev/null
+++ b/.trae/rules/git-commit-message.md
@@ -0,0 +1,11 @@
+---
+alwaysApply: true
+scene: git_message
+---
+
+在此处编写规则，自定义 AI 生成提交信息的风格。
+
+## 提交信息格式
+- 提交信息必须使用中文。
+- 提交信息必须包含变更的类型（例如 "fix"、"feat"、"refactor" 等）。
+- 提交信息必须尽简洁明了，不要超过一段落。
diff --git a/src/pyflowx/tasks/system.py b/src/pyflowx/tasks/system.py
index eb60dc4..73ea061 100644
--- a/src/pyflowx/tasks/system.py
+++ b/src/pyflowx/tasks/system.py
@@ -113,10 +113,7 @@ def write_file(path: str, content: str, encoding: str = "utf-8") -> px.TaskSpec:
     """写入文件任务."""
 
     def write():
-        try:
-            with open(path, "w", encoding=encoding) as f:
-                f.write(content)
-        except Exception as e:
-            print(f"写入文件 {path} 失败: {e}")
+        p = Path(path)
+        p.write_text(content, encoding=encoding)
 
     return px.TaskSpec(f"write_file_{path}", fn=write, verbose=True)
diff --git a/tests/test_conditions.py b/tests/test_conditions.py
index e8a371b..2e467f4 100644
--- a/tests/test_conditions.py
+++ b/tests/test_conditions.py
@@ -301,3 +301,59 @@ def test_dir_exists_false(tmp_path: Path):
     missing = tmp_path / "nonexistent"
     cond = BuiltinConditions.DIR_EXISTS(missing)
     assert cond({}) is False
+
+
+def test_builtin_is_windows_returns_module_condition():
+    """BuiltinConditions.IS_WINDOWS() 应返回模块级 IS_WINDOWS."""
+    assert BuiltinConditions.IS_WINDOWS() is IS_WINDOWS
+
+
+def test_builtin_is_linux_returns_module_condition():
+    """BuiltinConditions.IS_LINUX() 应返回模块级 IS_LINUX."""
+    assert BuiltinConditions.IS_LINUX() is IS_LINUX
+
+
+def test_builtin_is_macos_returns_module_condition():
+    """BuiltinConditions.IS_MACOS() 应返回模块级 IS_MACOS."""
+    assert BuiltinConditions.IS_MACOS() is IS_MACOS
+
+
+def test_builtin_is_posix_returns_module_condition():
+    """BuiltinConditions.IS_POSIX() 应返回模块级 IS_POSIX."""
+    assert BuiltinConditions.IS_POSIX() is IS_POSIX
+
+
+def test_file_content_exists_missing_file(tmp_path: Path):
+    """FILE_CONTENT_EXISTS 文件不存在时返回 False."""
+    cond = BuiltinConditions.FILE_CONTENT_EXISTS(tmp_path / "missing.txt", "x")
+    assert cond({}) is False
+
+
+def test_file_content_exists_contains_content(tmp_path: Path):
+    """FILE_CONTENT_EXISTS 文件包含内容时返回 True."""
+    f = tmp_path / "f.txt"
+    f.write_text("hello world", encoding="utf-8")
+    cond = BuiltinConditions.FILE_CONTENT_EXISTS(f, "world")
+    assert cond({}) is True
+
+
+def test_file_content_exists_not_contains_content(tmp_path: Path):
+    """FILE_CONTENT_EXISTS 文件不包含内容时返回 False."""
+    f = tmp_path / "f.txt"
+    f.write_text("hello", encoding="utf-8")
+    cond = BuiltinConditions.FILE_CONTENT_EXISTS(f, "missing")
+    assert cond({}) is False
+
+
+def test_file_content_exists_decode_error_returns_false(tmp_path: Path):
+    """FILE_CONTENT_EXISTS 读取非 UTF-8 文件应返回 False（解码异常被吞）."""
+    f = tmp_path / "bin.dat"
+    f.write_bytes(b"\xff\xfe\x00bad")
+    cond = BuiltinConditions.FILE_CONTENT_EXISTS(f, "x")
+    assert cond({}) is False
+
+
+def test_dep_matches_missing_dep_returns_false():
+    """DEP_MATCHES 依赖不存在时应返回 False（覆盖 if not in ctx 分支）."""
+    cond = BuiltinConditions.DEP_MATCHES("missing", lambda _v: True)
+    assert cond({}) is False
diff --git a/tests/test_graph.py b/tests/test_graph.py
index 17f2d58..8d2b0ac 100644
--- a/tests/test_graph.py
+++ b/tests/test_graph.py
@@ -319,6 +319,79 @@ def test_compose_function() -> None:
     assert "a1" in resolved["cmd_b"]
 
 
+def test_graph_composer_expand_refs_multiple_refs_chain() -> None:
+    """expand_refs 多个 ref 应串联依赖：后一个 ref 首任务依赖前一个 ref 末任务."""
+    graph_a = px.Graph.from_specs([px.TaskSpec("a1", _fn)])
+    graph_c = px.Graph.from_specs([px.TaskSpec("c1", _fn)])
+    graph_b = px.Graph.from_specs([px.TaskSpec("b1", _fn)])
+    graph_b._pending_refs = ["cmd_a", "cmd_c"]
+
+    composer = GraphComposer({"cmd_a": graph_a, "cmd_c": graph_c, "cmd_b": graph_b})
+    resolved = composer.resolve_all()
+
+    # c1 应依赖 a1（后 ref 首任务依赖前 ref 末任务）
+    assert "a1" in resolved["cmd_b"]
+    assert "c1" in resolved["cmd_b"]
+    assert "b1" in resolved["cmd_b"]
+    c1_spec = resolved["cmd_b"].all_specs()["c1"]
+    assert "a1" in c1_spec.depends_on
+
+
+def test_graph_composer_expand_refs_ref_returns_empty() -> None:
+    """expand_refs 引用空图时，previous_ref_last_task 保持 None，original_specs 走 else 分支."""
+    graph_empty = px.Graph.from_specs([])
+    graph_b = px.Graph.from_specs([px.TaskSpec("b1", _fn)])
+    graph_b._pending_refs = ["empty_cmd"]
+
+    composer = GraphComposer({"empty_cmd": graph_empty, "cmd_b": graph_b})
+    resolved = composer.resolve_all()
+
+    # b1 保留，无额外依赖
+    assert "b1" in resolved["cmd_b"]
+    b1_spec = resolved["cmd_b"].all_specs()["b1"]
+    assert b1_spec.depends_on == ()
+
+
+def test_graph_composer_expand_refs_multiple_original_specs_serialized() -> None:
+    """expand_refs 多个 original_specs 应串行依赖，且首个依赖 ref 末任务."""
+    graph_a = px.Graph.from_specs([px.TaskSpec("a1", _fn)])
+    graph_b = px.Graph.from_specs([
+        px.TaskSpec("b1", _fn),
+        px.TaskSpec("b2", _fn),
+        px.TaskSpec("b3", _fn),
+    ])
+    graph_b._pending_refs = ["cmd_a"]
+
+    composer = GraphComposer({"cmd_a": graph_a, "cmd_b": graph_b})
+    resolved = composer.resolve_all()
+
+    specs = resolved["cmd_b"].all_specs()
+    # b1 依赖 a1（ref 末任务）
+    assert "a1" in specs["b1"].depends_on
+    # b2 依赖 b1，b3 依赖 b2（串行）
+    assert "b1" in specs["b2"].depends_on
+    assert "b2" in specs["b3"].depends_on
+
+
+def test_graph_composer_parse_ref_dot_notation_success() -> None:
+    """parse_ref 'cmd.task' 形式应返回对应单个 TaskSpec."""
+    graph_a = px.Graph.from_specs([px.TaskSpec("a1", _fn), px.TaskSpec("a2", _fn)])
+    composer = GraphComposer({"cmd_a": graph_a})
+
+    result = composer.parse_ref("cmd_a.a2", "cmd_b")
+    assert len(result) == 1
+    assert result[0].name == "a2"
+
+
+def test_graph_composer_parse_ref_dot_notation_cmd_not_found() -> None:
+    """parse_ref 'missing.task' 形式应检测命令不存在."""
+    graph_a = px.Graph.from_specs([px.TaskSpec("a1", _fn)])
+    composer = GraphComposer({"cmd_a": graph_a})
+
+    with pytest.raises(ValueError, match="引用的命令 'missing' 不存在"):
+        _ = composer.parse_ref("missing.task", "cmd_b")
+
+
 # ---------------------------------------------------------------------- #
 # resolved_spec defaults 测试
 # ---------------------------------------------------------------------- #
diff --git a/tests/test_system.py b/tests/test_system.py
index be530a1..229f1b5 100644
--- a/tests/test_system.py
+++ b/tests/test_system.py
@@ -2,11 +2,12 @@
 
 import os
 import subprocess
+from pathlib import Path
 
 import pytest
 
 from pyflowx.conditions import Constants
-from pyflowx.tasks.system import clr, reset_icon_cache, setenv, which
+from pyflowx.tasks.system import clr, reset_icon_cache, setenv, setenv_group, which, write_file
 
 
 def test_clr_creates_task_spec() -> None:
@@ -189,3 +190,57 @@ def test_which_not_found(monkeypatch: pytest.MonkeyPatch, capsys: pytest.Capture
     spec.fn()
     captured = capsys.readouterr()
     assert "nonexistent_cmd -> 未找到" in captured.out
+
+
+def test_write_file_creates_task_spec() -> None:
+    """write_file() 应创建带 verbose 的 TaskSpec。"""
+    spec = write_file("/tmp/unused", "x")
+    assert spec.name == "write_file_/tmp/unused"
+    assert spec.verbose is True
+
+
+def test_write_file_writes_content(tmp_path: Path) -> None:
+    """write_file() 应将内容写入指定文件."""
+    f = tmp_path / "out.txt"
+    spec = write_file(str(f), "hello world")
+    assert spec.fn is not None
+    spec.fn()
+    assert f.read_text(encoding="utf-8") == "hello world"
+
+
+def test_write_file_with_encoding(tmp_path: Path) -> None:
+    """write_file() 应支持指定编码."""
+    f = tmp_path / "out.txt"
+    spec = write_file(str(f), "中文", encoding="utf-8")
+    assert spec.fn is not None
+    spec.fn()
+    assert f.read_text(encoding="utf-8") == "中文"
+
+
+def test_write_file_failure_propagates(tmp_path: Path) -> None:
+    """write_file() 写入失败应抛出异常（不吞异常）."""
+    # 父目录不存在时写入应抛 FileNotFoundError
+    missing = tmp_path / "no_such_dir" / "out.txt"
+    spec = write_file(str(missing), "x")
+    assert spec.fn is not None
+    with pytest.raises(FileNotFoundError):
+        spec.fn()
+
+
+def test_setenv_group_creates_specs() -> None:
+    """setenv_group() 应为每个环境变量创建 TaskSpec."""
+    envs = {"VAR_A": "1", "VAR_B": "2"}
+    specs = setenv_group(envs)
+    assert len(specs) == 2
+    assert specs[0].name == "setenv_var_a"
+    assert specs[1].name == "setenv_var_b"
+
+
+def test_setenv_group_default_mode(monkeypatch: pytest.MonkeyPatch) -> None:
+    """setenv_group(default=True) 不应覆盖已存在的环境变量."""
+    monkeypatch.setenv("PYFLOWX_GROUP_EXISTS", "original")
+    specs = setenv_group({"PYFLOWX_GROUP_EXISTS": "new"}, default=True)
+    for spec in specs:
+        assert spec.fn is not None
+        spec.fn()
+    assert os.environ["PYFLOWX_GROUP_EXISTS"] == "original"