Monkeypatch setenv doesn't work in default value for function parameter

[OwenMatsuda]

Using:
pytest==5.3.5
pytest-mock==2.0.0
pytest-sugar==0.9.2

It seems that monkeypatch.setenv doesn't work when os.getenv is the default value for a function parameter. I would expect stdout to say "garbage" both times.

def my_test(port=os.getenv("PORT")):
 print(port)
 print(os.getenv("PORT"))

def test_port_env_fail(monkeypatch):
 monkeypatch.setenv("PORT", "garbage")
 my_test()
 raise Exception("fail")

[OwenMatsuda]

Not a monkeypatch problem. The same happens with the following:

def my_test(port=os.getenv("PORT")):
 print(port)
 print(os.getenv("PORT"))

def test_port_env_fail(monkeypatch):
 os.environ["PORT"] = "garbage"
 print(os.getenv("PORT"))
 my_test()
 raise Exception("fail")