Python 2.x: How to mock subprocess.Popen if stdin=PIPE

Question

I am trying to mock below function

from subprocess import Popen, PIPE    
def run_query():
    sql_cmd = "Some Query"
    process = Popen(["sqlplus", "-S", "/", "as", "sysdba"], stdin=PIPE, stdout=PIPE, stderr=PIPE)
    process.stdin.write(sql_cmd)
    (process_stdout, process_stderr) = process.communicate()

Below is the test function I wrote:

@patch('subprocess.Popen')
def test_run_query(Popen):
    Popen.return_value.communicate.return_value = (2, 1)

However, I am getting below error

Error occured while running sql command
Error output:
[Errno 2] No such file or directory
F

I tried other stackoverflow post but this kind of example is not there. Any help please.

Answer 1

You are patching Popen within the wrong namespace.

You need to patch the name Popen in the namespace where it is looked up, not where it is defined. Assuming mypackage/mymodule.py is the module in which run_query is defined:

from mypackage.mymodule import run_query

@patch('mypackage.mymodule.Popen')
def test_run_query(mock_popen):
    proc = mock_popen.return_value
    proc.communicate.return_value = "2", "1"
    out, err = run_query()
    assert out == "2"
    assert err == "1"
    proc.stdin.write.assert_called_once_with("Some Query")

See Where to patch in the mock documentation for more info.