Using Mocking for unit testing in python

Question

I have two functions in a python file. I want to do some unit tests for these functions using Mock.

def col_rename(col_name):
    reps = ((' ', '_&'), ('(', '*_'), (')', '_*'), ('{', '#_'), ('}', '_#'))
    new_cols = reduce(lambda a, kv: a.replace(*kv), reps, col_name)
    return new_cols

def rename_characters(df):
    df_cols = df.schema.names
    for x in df_cols:
        df = df.withColumnRenamed(x, col_rename(x))
    return df

In the above function withColumnRenamed is a function in pyspark that will return a column after is renames the column name. df is a pyspark data frame.

I am able to do unit testing to the col_rename function.

I am able to do unit testing to the rename_characters function by creating data frames manually in pyspark.

Now I want to do the unit testing using Mock in python.

I have tried something like this below. I am not sure if this is correct or What I am doing is completely wrong

import unittest
from mock import patch

class Test(unittest.TestCase):
    @patch('mymodule.rename_characters')
    def test_func(self, rename_characters_mock):
        rename_characters_mock.return_value = 'mocked values'
        self.assertEqual(return_value, 'mocked_values'))

How can I do Mocking for the unit testing as in the above scenario

from mymodule import rename_characters, r u sure we can import a func? — Gang
– Gang, Commented Mar 15, 2018 at 2:39
@Gang In pycharm it gave me unused import statement error, I removed the import statement — User12345
– User12345, Commented Mar 15, 2018 at 2:46
almost there. it makes more sense if you want to mock pyspark.x, self.assertEqual(return_value, 'mocked_values')) the return_value is not defined, are u try to self.assertEqual(mymodule.rename_charaters(), 'mocked_value' ? — Gang
– Gang, Commented Mar 15, 2018 at 2:52
@Gang I want to try self.assertEqual(mymodule.rename_charaters(), 'mocked_value' — User12345
– User12345, Commented Mar 15, 2018 at 3:00

Gang · Accepted Answer · 2018-03-15 03:13:30Z

1

you might need this

import mymodule

Outside Test class define a local function

def local_rename_characters():
    return 'mocked_local_values'

This should work

@patch('mymodule.rename_characters')
def test_func(self, rename_characters_mock):
    rename_characters_mock.return_value = 'mocked values'
    self.assertEqual(mymodule.rename_characters(), 'mocked_values')

Alternatives using side_effect

@patch('mymodule.rename_characters')
def test_func(self, rename_characters_mock):
    rename_characters_mock.side_effect = local_rename_characters
    self.assertEqual(mymodule.rename_characters(), 'mocked_local_values')

answered Mar 15, 2018 at 3:13

Gang

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3 Comments

User12345 Over a year ago

If I want to mock the withColumnRenamed method that is inside the rename_characters function how can I do that

Gang Over a year ago

DataFrame instance is already a variable, u do not really need to mock. but if u do want to play and learn, @patch('mymodule.pyspark.sql.DataFrame.withColumnRenamed') and then mocked_withColumRenamed.side_effect = local_create_dummy_df, using createDataFrame

User12345 Over a year ago

could you please have a look at https://stackoverflow.com/questions/49420660/unit-test-pyspark-code-using-python

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