style: pre-commit fixes

Author: pre-commit-ci[bot]

docs/pages/principles/testing.md

@@ -337,12 +337,12 @@ These are a few of the cases that cause the most confusion.
 ```python
 # src.lib
 def dangerous_sideffects():
-    raise RuntimeError('BOOM')
+    raise RuntimeError("BOOM")
 
 
 def say_hello():
     dangerous_sideffects()
-    return 'hello world'
+    return "hello world"
 ```
 
 ```python
@@ -351,11 +351,11 @@ from src.lib import say_hello, dangerous_sideffects
 
 def test_pytest(mocker):
     # Given this context
-    mock_say_hello = mocker.patch('src.lib.dangerous_sideffects')
+    mock_say_hello = mocker.patch("src.lib.dangerous_sideffects")
     # When we run the code
     ret = say_hello()
     # Then we expect the result
-    assert ret == 'hello world'
+    assert ret == "hello world"
     mock_dangerous_sideffects.assert_called_once()
 
     # But this will still raise an exception!