assert_called() raising exception even though class was instantiated

Using this answer as a model, I am testing the following method that instantiates a class (EmailMultiAlternatives):

admintools/emailer.py

from django.core.mail import EmailMultiAlternatives
from django.template.loader import render_to_string
from django.utils.html import strip_tags


def send_email(template_path, context, subject_line, from_email, to=[], cc=[], bcc=DEFAULT_BCC_EMAILS):
    msg_html = render_to_string(template_path, context)
    msg_plain = strip_tags(msg_html)
    email = EmailMultiAlternatives(subject_line, msg_plain, from_email, to, cc=cc, bcc=bcc)
    email.attach_alternative(msg_html, "text/html")
    email.send()

using test.py:

from unittest.mock import patch

from django.core.mail import EmailMultiAlternatives
from django.template.loader import render_to_string
from django.test import TestCase

from admintools.emailer import send_email
from admintools.settings import DEFAULT_BCC_EMAILS


class EmailerTestCase(TestCase):

    @patch('django.core.mail.EmailMultiAlternatives')
    def test_send_email(self, mockEmailMultiAlternatives):
        context = {}
        template_path = "emails/closings/seller_pre_close_update_prompt.html"
        msg_plain = render_to_string(template_path, context)
        to = ['']
        cc = ['']
        send_email(template_path, {}, 'subject', "from", to, cc=cc)
        mockEmailMultiAlternatives.assert_called()

I receive AssertionError: Expected 'EmailMultiAlternatives' to have been called. even though email is created successfully during the running of the test (verified by a print(email) immediately after the instantiation returning <django.core.mail.message.EmailMultiAlternatives object at 0x7fbf4bb4b590>).

What might be causing the assertion to fail even though EmailMultiAlternatives is being instantiated?