[test] add user agent test suite and fix typo.

kernels/src/kernels/utils.py

@@ -592,7 +592,7 @@ def _get_hf_api(user_agent: str | dict | None = None) -> HfApi:
         # System info
         python = ".".join(platform.python_version_tuple()[:2])
         backend = _select_backend(None).variant_str
-        user_agent_str += f"; kernels/{__version__}; python/{python}; backend/{backend}; flatform/{_platform()}; file_type/kernel"
+        user_agent_str += f"; kernels/{__version__}; python/{python}; backend/{backend}; platform/{_platform()}; file_type/kernel"
 
         if has_torch:
             import torch

kernels/tests/test_user_agent.py

@@ -0,0 +1,71 @@
+import platform
+
+from kernels.utils import _get_hf_api, _platform
+
+
+def test_user_agent_contains_core_fields():
+    api = _get_hf_api()
+    ua = api.user_agent
+
+    assert "kernels/" in ua
+    python_ver = ".".join(platform.python_version_tuple()[:2])
+    assert f"python/{python_ver}" in ua
+    assert "backend/" in ua
+    assert f"platform/{_platform()}" in ua
+    assert "file_type/kernel" in ua
+
+
+def test_user_agent_with_string():
+    api = _get_hf_api(user_agent="my-app/1.0")
+    ua = api.user_agent
+
+    assert "my-app/1.0" in ua
+    assert "kernels/" in ua
+
+
+def test_user_agent_with_dict():
+    api = _get_hf_api(user_agent={"app": "test", "ver": "2.0"})
+    ua = api.user_agent
+
+    assert "app/test" in ua
+    assert "ver/2.0" in ua
+    assert "kernels/" in ua
+
+
+def test_user_agent_telemetry_disabled(monkeypatch):
+    from huggingface_hub import constants
+
+    monkeypatch.setattr(constants, "HF_HUB_DISABLE_TELEMETRY", True)
+    api = _get_hf_api(user_agent="should-not-appear")
+    assert api.user_agent == ""
+
+
+def test_user_agent_includes_torch():
+    api = _get_hf_api()
+    ua = api.user_agent
+
+    # If torch is importable, it should appear in the UA.
+    try:
+        import torch
+
+        assert f"torch/{torch.__version__}" in ua
+    except ImportError:
+        assert "torch/" not in ua
+
+
+def test_user_agent_format_structure():
+    api = _get_hf_api()
+    ua = api.user_agent
+
+    fields = [f.strip() for f in ua.split(";") if f.strip()]
+    # Each field should be key/value
+    for field in fields:
+        assert "/" in field, f"Field missing key/value separator: {field}"
+
+
+def test_platform_format():
+    plat = _platform()
+    assert "-" in plat
+    parts = plat.split("-")
+    assert len(parts) == 2
+    assert parts[1] in ("linux", "darwin", "windows")