I am writing unit tests for my trading bot and can not figure out why, when I call a method belonging to a mocked class object, the dataframe being passed inside the method call is not being altered as per method definition and/or not being altered at all.

import pytest
from unittest.mock import MagicMock
import technical_analysis_manager_dir
from bot import Bot
from testing.sample_data_manager  import big_sample_dataframe


def test_get_close_candidates_nearest_open(big_sample_dataframe):

    update_date = '2024-03-18 12:54:00.000'  # This is the date of the row whose divergence open value is being
    # updated, to ensure later rows will have a pair

    evaluation_date = '2024-03-18 13:26:00.000'  # This is the date of the row whose divergence open value is being
    # evaluated

    # Create a sample dataframe via big_sample_dataframe
    symbol = 'symbol'
    sample_data = {symbol: big_sample_dataframe}

    # Set the 'is_divergence_open_candidate' value == 1, at the update date
    # Learning: What is the syntax to access a pandas dataframe row+column value?
    # Answer: First select the dataframe, for this use case it is: sample_data['symbol']. Next call the loc method
    # with: .loc[] (label based indexing). Inside the .loc[] property, specify a row and column label. Note: in the
    # use case below, we conditionally select the row where the ['Date']  == update_date
    sample_data['symbol'].loc[sample_data['symbol']['Date'] == update_date, 'is_divergence_open_candidate'] = 1

"""
------------------
Attention: This is what is working
------------------
"""


    # Create an instance of DivergenceCalculator
    divergence_calculator_instance = technical_analysis_manager_dir.DivergenceCalculator()

    # Call the get_close_candidates_nearest_open method
    divergence_calculator_instance.get_close_candidates_nearest_open(sample_data['symbol'], row_number=-1)
"""
------------------
End of what is what is working
------------------
"""

"""
------------------
Attention: This is what did NOT work
------------------
"""
    # Learning: Here the 'spec=' keyword informs the MagicMock class constructor which object is being mocked. It
    # therefore defines which methods and attributes that the mocked object should have.
    mocked_divergence_calculator = MagicMock(spec=technical_analysis_manager_dir.DivergenceCalculator)

    # Configure the return value of the mocked method
    mocked_divergence_calculator.get_close_candidates_nearest_open.return_value = sample_data['symbol']

    # Call the get_open_candidate method
    mocked_divergence_calculator.get_close_candidates_nearest_open(sample_data, row_number=-1)
"""
------------------
End of what did NOT work
------------------
"""


    print(sample_data['symbol'].loc[sample_data['symbol']['Date']== update_date, 'is_divergence_open_candidate'])
    # Select the row which contains the target date (for later test assertion)
    evaluation_df = sample_data['symbol'].loc[sample_data['symbol']['Date'] == evaluation_date]
    print(evaluation_df)
    print(evaluation_df['paired_divergence_opens_id'].iloc[-1])
    # Learning: Why do I need to specify [0] in the below iloc call (integer based indexing)
    # Answer: Every call of the '.iloc' property requires an integer to specify the row and then column. Example
    # syntax: df.iloc[1, 0] will access the second [1] row, of the first [0] column. In the below use case we specify
    # the column by label, so we only need to specify the row by integer, i.e. [0]
    assert evaluation_df['paired_divergence_opens_id'].iloc[-1] == 128

As per the code block you can see what I had tried (with MagicMock()). I do not understand why it failed :/