如何模拟 psycopg2 光标对象?

How to mock psycopg2 cursor object?(如何模拟 psycopg2 光标对象?)

问题描述

我在 Python2 中有这个代码段:

I have this code segment in Python2:

def super_cool_method():
    con = psycopg2.connect(**connection_stuff)
    cur = con.cursor(cursor_factory=DictCursor)
    cur.execute("Super duper SQL query")
    rows = cur.fetchall()

    for row in rows:
        # do some data manipulation on row
    return rows

我想为其编写一些单元测试.我想知道如何使用 mock.patch 来修补游标和连接变量，以便它们返回一组假数据?我已经为我的单元测试尝试了以下代码段，但无济于事:

that I'd like to write some unittests for. I'm wondering how to use mock.patch in order to patch out the cursor and connection variables so that they return a fake set of data? I've tried the following segment of code for my unittests but to no avail:

@mock.patch("psycopg2.connect")
@mock.patch("psycopg2.extensions.cursor.fetchall")
def test_super_awesome_stuff(self, a, b):
    testing = super_cool_method()

但我似乎收到以下错误:

But I seem to get the following error:

TypeError: can't set attributes of built-in/extension type 'psycopg2.extensions.cursor'

推荐答案

由于游标是con.cursor的返回值，所以只需要mock连接，然后正确配置即可.例如，

Since the cursor is the return value of con.cursor, you only need to mock the connection, then configure it properly. For example,

query_result = [("field1a", "field2a"), ("field1b", "field2b")]
with mock.patch('psycopg2.connect') as mock_connect:
    mock_connect.cursor.return_value.fetchall.return_value = query_result
    super_cool_method()

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