用過unittest的朋友，肯定知道可以藉助DDT實現引數化。用過JMeter的朋友，肯定知道JMeter自帶了4種引數化方式（見參考資料）。pytest同樣支援引數化，而且很簡單很實用。 # 語法 在《pytest封神之路第三步 精通fixture》和《pytest封神之路第四步 內建和自定義marker》兩篇文章中，都提到了pytest引數化。那麼本文就趁著熱乎，趕緊聊一聊pytest的引數化是怎麼玩的。 **@pytest.mark.parametrize** ```python @pytest.mark.parametrize("test_input,expected", [("3+5", 8), ("2+4", 6), ("6*9", 42)]) def test_eval(test_input, expected): assert eval(test_input) == expected ``` - 可以自定義變數，test_input對應的值是"3+5" "2+4" "6\*9"，expected對應的值是8 6 42，**多個變數用tuple，多個tuple用list** - 引數化的變數是引用而非複製，意味著如果值是list或dict，改變值會影響後續的test - 重疊產生笛卡爾積 ```python import pytest @pytest.mark.parametrize("x", [0, 1]) @pytest.mark.parametrize("y", [2, 3]) def test_foo(x, y): pass ``` **@pytest.fixture()** ```python @pytest.fixture(scope="module", params=["smtp.gmail.com", "mail.python.org"]) def smtp_connection(request): smtp_connection = smtplib.SMTP(request.param, 587, timeout=5) ``` - 只能使用request.param來引用 - 引數化生成的test帶有ID，可以使用`-k`來篩選執行。預設是根據`函式名[引數名]`來的，可以使用ids來定義 ```python // list @pytest.fixture(params=[0, 1], ids=["spam", "ham"]) // function @pytest.fixture(params=[0, 1], ids=idfn) ``` 使用`--collect-only `命令列引數可以看到生成的IDs。 **引數新增marker** 我們知道了引數化後會生成多個tests，如果有些test需要marker，可以用pytest.param來新增 marker方式 ```python # content of test_expectation.py import pytest @pytest.mark.parametrize( "test_input,expected", [("3+5", 8), ("2+4", 6), pytest.param("6*9", 42, marks=pytest.mark.xfail)], ) def test_eval(test_input, expected): assert eval(test_input) == expected ``` fixture方式 ```python # content of test_fixture_marks.py import pytest @pytest.fixture(params=[0, 1, pytest.param(2, marks=pytest.mark.skip)]) def data_set(request): return request.param def test_data(data_set): pass ``` **pytest_generate_tests** 用來自定義引數化方案。使用到了hook，hook的知識我會寫在《pytest hook》中，歡迎關注公眾號dongfanger獲取最新文章。 ```python # content of conf.py def pytest_generate_tests(metafunc): if "test_input" in metafunc.fixturenames: metafunc.parametrize("test_input", [0, 1]) ``` ```python # content of test.py def test(test_input): assert test_input == 0 ``` - 定義在conftest.py檔案中 - metafunc有5個屬性，fixturenames，module，config，function，cls - metafunc.parametrize() 用來實現引數化 - 多個metafunc.parametrize() 的引數名不能重複，否則會報錯 # 引數化誤區 在講示例之前，先簡單分享我的菜雞行為。假設我們現在需要對50個介面測試，驗證某一角色的使用者訪問這些介面會返回403。我的做法是，把介面請求全部引數化了，test函式裡面只有斷言，**虛擬碼**大致如下 ```python def api(): params = [] def func(): return request() params.append(func) ... @pytest.mark.parametrize('req', api()) def test(): res = req() assert res.status_code == 403 ``` 這樣引數化以後，會產生**50個tests**，如果斷言失敗了，會單獨標記為failed，不影響其他test結果。咋一看還行，但是有個問題，在迴歸的時候，可能只需要驗證其中部分介面，就沒有辦法靈活的調整，必須全部跑一遍才行。這是一個**相對錯誤的示範**，至於正確的應該怎麼寫，相信每個人心中都有一個答案，能解決問題就是ok的。我想表達的是，**引數化要適當，不要濫用，最好只對測試資料做引數化**。 # 實踐 本文的**重點**來了，引數化的語法比較簡單，實際應用是關鍵。這部分通過11個例子，來實踐一下。**示例覆蓋的知識點有點多，建議留大段時間細看。** 1.使用hook新增命令列引數--all，"param1"是引數名，帶--all引數時是range(5) == [0, 1, 2, 3, 4]，生成5個tests。不帶引數時是range(2)。 ```python # content of test_compute.py def test_compute(param1): assert param1 < 4 ``` ```python # content of conftest.py def pytest_addoption(parser): parser.addoption("--all", action="store_true", help="run all combinations") def pytest_generate_tests(metafunc): if "param1" in metafunc.fixturenames: if metafunc.config.getoption("all"): end = 5 else: end = 2 metafunc.parametrize("param1", range(end)) ``` 2.testdata是測試資料，包括2組。test_timedistance_v0不帶ids。test_timedistance_v1帶list格式的ids。test_timedistance_v2的ids為函式。test_timedistance_v3使用pytest.param同時定義測試資料和id。 ```python # content of test_time.py from datetime import datetime, timedelta import pytest testdata = [ (datetime(2001, 12, 12), datetime(2001, 12, 11), timedelta(1)), (datetime(2001, 12, 11), datetime(2001, 12, 12), timedelta(-1)), ] @pytest.mark.parametrize("a,b,expected", testdata) def test_timedistance_v0(a, b, expected): diff = a - b assert diff == expected @pytest.mark.parametrize("a,b,expected", testdata, ids=["forward", "backward"]) def test_timedistance_v1(a, b, expected): diff = a - b assert diff == expected def idfn(val): if isinstance(val, (datetime,)): # note this wouldn't show any hours/minutes/seconds return val.strftime("%Y%m%d") @pytest.mark.parametrize("a,b,expected", testdata, ids=idfn) def test_timedistance_v2(a, b, expected): diff = a - b assert diff == expected @pytest.mark.parametrize( "a,b,expected", [ pytest.param( datetime(2001, 12, 12), datetime(2001, 12, 11), timedelta(1), id="forward" ), pytest.param( datetime(2001, 12, 11), datetime(2001, 12, 12), timedelta(-1), id="backward" ), ], ) def test_timedistance_v3(a, b, expected): diff = a - b assert diff == expected ``` 3.相容unittest的testscenarios ```python # content of test_scenarios.py def pytest_generate_tests(metafunc): idlist = [] argvalues = [] for scenario in metafunc.cls.scenarios: idlist.append(scenario[0]) items = scenario[1].items() argnames = [x[0] for x in items] argvalues.append([x[1] for x in items]) metafunc.parametrize(argnames, argvalues, ids=idlist, scope="class") scenario1 = ("basic", {"attribute": "value"}) scenario2 = ("advanced", {"attribute": "value2"}) class TestSampleWithScenarios: scenarios = [scenario1, scenario2] def test_demo1(self, attribute): assert isinstance(attribute, str) def test_demo2(self, attribute): assert isinstance(attribute, str) ``` 4.初始化資料庫連線 ```python # content of test_backends.py import pytest def test_db_initialized(db): # a dummy test if db.__class__.__name__ == "DB2": pytest.fail("deliberately failing for demo purposes") ``` ```python # content of conftest.py import pytest def pytest_generate_tests(metafunc): if "db" in metafunc.fixturenames: metafunc.parametrize("db", ["d1", "d2"], indirect=True) class DB1: "one database object" class DB2: "alternative database object" @pytest.fixture def db(request): if request.param == "d1": return DB1() elif request.param == "d2": return DB2() else: raise ValueError("invalid internal test config") ``` 5.如果不加indirect=True，會生成2個test，fixt的值分別是"a"和"b"。如果加了indirect=True，會先執行fixture，fixt的值分別是"aaa"和"bbb"。indirect=True結合fixture可以在生成test前，對引數變數額外處理。 ```python import pytest @pytest.fixture def fixt(request): return request.param * 3 @pytest.mark.parametrize("fixt", ["a", "b"], indirect=True) def test_indirect(fixt): assert len(fixt) == 3 ``` 6.多個引數時，indirect賦值list可以指定某些變數應用fixture，沒有指定的保持原值。 ```python # content of test_indirect_list.py import pytest @pytest.fixture(scope="function") def x(request): return request.param * 3 @pytest.fixture(scope="function") def y(request): return request.param * 2 @pytest.mark.parametrize("x, y", [("a", "b")], indirect=["x"]) def test_indirect(x, y): assert x == "aaa" assert y == "b" ``` 7.相容unittest引數化 ```python # content of ./test_parametrize.py import pytest def pytest_generate_tests(metafunc): # called once per each test function funcarglist = metafunc.cls.params[metafunc.function.__name__] argnames = sorted(funcarglist[0]) metafunc.parametrize( argnames, [[funcargs[name] for name in argnames] for funcargs in funcarglist] ) class TestClass: # a map specifying multiple argument sets for a test method params = { "test_equals": [dict(a=1, b=2), dict(a=3, b=3)], "test_zerodivision": [dict(a=1, b=0)], } def test_equals(self, a, b): assert a == b def test_zerodivision(self, a, b): with pytest.raises(ZeroDivisionError): a / b ``` 8.在不同python直譯器之間測試物件序列化。python1把物件pickle-dump到檔案。python2從檔案中pickle-load物件。 ```python """ module containing a parametrized tests testing cross-python serialization via the pickle module. """ import shutil import subprocess import textwrap import pytest pythonlist = ["python3.5", "python3.6", "python3.7"] @pytest.fixture(params=pythonlist) def python1(request, tmpdir): picklefile = tmpdir.join("data.pickle") return Python(request.param, picklefile) @pytest.fixture(params=pythonlist) def python2(request, python1): return Python(request.param, python1.picklefile) class Python: def __init__(self, version, picklefile): self.pythonpath = shutil.which(version) if not self.pythonpath: pytest.skip("{!r} not found".format(version)) self.picklefile = picklefile def dumps(self, obj): dumpfile = self.picklefile.dirpath("dump.py") dumpfile.write( textwrap.dedent( r""" import pickle f = open({!r}, 'wb') s = pickle.dump({!r}, f, protocol=2) f.close() """.format( str(self.picklefile), obj ) ) ) subprocess.check_call((self.pythonpath, str(dumpfile))) def load_and_is_true(self, expression): loadfile = self.picklefile.dirpath("load.py") loadfile.write( textwrap.dedent( r""" import pickle f = open({!r}, 'rb') obj = pickle.load(f) f.close() res = eval({!r}) if not res: raise SystemExit(1) """.format( str(self.picklefile), expression ) ) ) print(loadfile) subprocess.check_call((self.pythonpath, str(loadfile))) @pytest.mark.parametrize("obj", [42, {}, {1: 3}]) def test_basic_objects(python1, python2, obj): python1.dumps(obj) python2.load_and_is_true("obj == {}".format(obj)) ``` 9.假設有個API，basemod是原始版本，optmod是優化版本，驗證二者結果一致。 ```python # content of conftest.py import pytest @pytest.fixture(scope="session") def basemod(request): return pytest.importorskip("base") @pytest.fixture(scope="session", params=["opt1", "opt2"]) def optmod(request): return pytest.importorskip(request.param) ``` ```python # content of base.py def func1(): return 1 ``` ```python # content of opt1.py def func1(): return 1.0001 ``` ```python # content of test_module.py def test_func1(basemod, optmod): assert round(basemod.func1(), 3) == round(optmod.func1(), 3) ``` 10.使用pytest.param新增marker和id。 ```python # content of test_pytest_param_example.py import pytest @pytest.mark.parametrize( "test_input,expected", [ ("3+5", 8), pytest.param("1+7", 8, marks=pytest.mark.basic), pytest.param("2+4", 6, marks=pytest.mark.basic, id="basic_2+4"), pytest.param( "6*9", 42, marks=[pytest.mark.basic, pytest.mark.xfail], id="basic_6*9" ), ], ) def test_eval(test_input, expected): assert eval(test_input) == expected ``` 11.使用pytest.raises讓部分test丟擲Error。 ```python from contextlib import contextmanager import pytest // 3.7+ from contextlib import nullcontext as does_not_raise @contextmanager def does_not_raise(): yield @pytest.mark.parametrize( "example_input,expectation", [ (3, does_not_raise()), (2, does_not_raise()), (1, does_not_raise()), (0, pytest.raises(ZeroDivisionError)), ], ) def test_division(example_input, expectation): """Test how much I know division.""" with expectation: assert (6 / example_input) is not None ``` # 簡要回顧 本文先講了引數化的語法，包括marker，fixture，hook方式，以及如何給引數新增marker，然後重點列舉了幾個實戰示例。引數化用好了能節省編碼，達到事半功倍的效果。 *參考資料* docs-pytest-org-en-stable JMeter4種引數化方式，請閱讀公眾號《三道題加油站