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"source": [
"# Mock\n",
"\n",
"[Mock-Objekte](https://de.wikipedia.org/wiki/Mock-Objekt) fördern Tests, die auf dem Verhalten von Objekten basieren. Die Python-Bibliothek [mock](https://docs.python.org/3/library/unittest.mock.html) ermöglicht euch, Teile des zu testenden Systems durch Scheinobjekte zu ersetzen und Aussagen über deren Verwendung zu treffen."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Installation\n",
"\n",
"[mock](https://docs.python.org/3/library/unittest.mock.html) ist seit Python 3.3 in der Python-Standardbibliothek enthalten. Für ältere Versionen von Python könnt ihr sie installieren mit:\n",
"\n",
"```bash\n",
"$ bin/python -m pip install mock\n",
"```"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Beispiel\n",
"\n",
"In unserem Beispiel wollen wir prüfen, ob die Arbeitstage von Montag bis Freitag korrekt ermittelt werden."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"1. Zunächst importieren wir `datetime` und `Mock`:"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [],
"source": [
"from datetime import datetime\n",
"from unittest.mock import Mock"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"2. Dann definieren wir zwei Testtage:"
]
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{
"cell_type": "code",
"execution_count": 2,
"metadata": {},
"outputs": [],
"source": [
"monday = datetime(year=2021, month=10, day=11)\n",
"saturday = datetime(year=2021, month=10, day=16)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"3. Nun definieren wir eine Methode zur Überprüfung der Arbeitstage, wobei die `datetime`-Bibliothek von Python Montage als `0` und Sonntage als `6` behandelt:"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {},
"outputs": [],
"source": [
"def is_workingday():\n",
" today = datetime.today()\n",
" return (0 <= today.weekday() < 5)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"4. Dann mocken wir `datetime`:"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {},
"outputs": [],
"source": [
"datetime = Mock()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"5. Schließlich testen wir unsere beiden Mock-Objekte:"
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {},
"outputs": [],
"source": [
"datetime.today.return_value = monday\n",
"assert is_workingday()"
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {},
"outputs": [],
"source": [
"datetime.today.return_value = saturday\n",
"assert not is_workingday()"
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {},
"outputs": [
{
"ename": "AssertionError",
"evalue": "",
"output_type": "error",
"traceback": [
"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[0;31mAssertionError\u001b[0m Traceback (most recent call last)",
"Cell \u001b[0;32mIn[7], line 2\u001b[0m\n\u001b[1;32m 1\u001b[0m datetime\u001b[38;5;241m.\u001b[39mtoday\u001b[38;5;241m.\u001b[39mreturn_value \u001b[38;5;241m=\u001b[39m monday\n\u001b[0;32m----> 2\u001b[0m \u001b[38;5;28;01massert\u001b[39;00m \u001b[38;5;129;01mnot\u001b[39;00m is_workingday()\n",
"\u001b[0;31mAssertionError\u001b[0m: "
]
}
],
"source": [
"datetime.today.return_value = monday\n",
"assert not is_workingday()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"\n",
"\n",
"**Siehe auch:**\n",
"\n",
"* [Introducing time-machine, a New Python Library for Mocking the Current Time](https://adamj.eu/tech/2020/06/03/introducing-time-machine/)\n",
"
"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## `mock.ANY`\n",
"\n",
"Mit [mock.ANY](https://docs.python.org/3/library/unittest.mock.html#any) könnt ihr prüfen, ob ein Wert überhaupt vorhanden ist, ohne einen genauen Wert prüfen zu müssen:"
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {},
"outputs": [],
"source": [
"from unittest.mock import ANY\n",
"\n",
"\n",
"mock = Mock(return_value=None)\n",
"mock(\"foo\", bar=object())\n",
"mock.assert_called_once_with(\"foo\", bar=ANY) "
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"\n",
"\n",
"**Hinweis:**\n",
"\n",
"In [test_report.py](https://github.com/openstack/zun/blob/917868f5fe02ff419fd35c5d9332f45a064ed385/zun/tests/unit/scheduler/client/test_report.py) des OpenStack Containerdienstes Zun findet ihr weitere praktische Beispiele für `ANY`.\n",
"
"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## `patch`-Dekorator\n",
"\n",
"Um Mock-Klassen oder Objekte zu erzeugen, kann der `patch`-Dekorator verwendet werden. In den folgenden Beispielen wird die Ausgabe von `os.listdir` gemockt. Dazu muss die Datei `example.txt` nicht im Verzeichnis vorhanden sein:"
]
},
{
"cell_type": "code",
"execution_count": 9,
"metadata": {},
"outputs": [],
"source": [
"import os\n",
"\n",
"from unittest import mock"
]
},
{
"cell_type": "code",
"execution_count": 10,
"metadata": {},
"outputs": [],
"source": [
"@mock.patch(\"os.listdir\", mock.MagicMock(return_value=\"example.txt\"))\n",
"def test_listdir():\n",
" assert \"example.txt\" == os.listdir()\n",
"\n",
"\n",
"test_listdir()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Alternativ kann der Rückgabewert auch separat definiert werden:"
]
},
{
"cell_type": "code",
"execution_count": 11,
"metadata": {},
"outputs": [],
"source": [
"@mock.patch(\"os.listdir\")\n",
"def test_listdir(mock_listdir):\n",
" mock_listdir.return_value = \"example.txt\"\n",
" assert \"example.txt\" == os.listdir()\n",
"\n",
"\n",
"test_listdir()"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"\n",
"\n",
"**Hinweis:**\n",
"\n",
"Mit [responses](https://github.com/getsentry/responses) könnt ihr Mock-Objekte für die [httpx](https://www.python4data.science/de/latest/data-processing/httpx/index.html)-Bibliothek erstellen.\n",
"
"
]
}
],
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"bibliofile": "biblio.bib",
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