Plotly graphs not rendered in extras data

[Sauci]

I'm trying to add Plotly graphs in my test report, but they are somehow not visible when I open the report (either Chrome or Edge).

To reproduce, two files need to be created: conftest.py and test_dummy_plot.py. Bellow, the content of those two files, respectively:

import pytest
import pytest_html


@pytest.mark.hookwrapper
def pytest_runtest_makereport(item, call):
    outcome = yield
    report = outcome.get_result()
    if call.when == 'call':
        extras = getattr(report, 'extras', [])
        fig = item.user_properties[0]
        c = fig.to_html(full_html=False, div_id='my_plot', include_plotlyjs='cdn')

        fig.write_html('my_plot.html', include_plotlyjs='cdn')  # export the figure to HTML to validate its content (just for debugging).

        extras.append(pytest_html.extras.html("<div>Additional HTML 1</div>"))  # only for debugging.
        extras.append(pytest_html.extras.html(c))
        extras.append(pytest_html.extras.html("<div>Additional HTML 2</div>"))  # only for debugging.
        report.extras = extras

import plotly.graph_objects as go
import pytest
from plotly.subplots import make_subplots


def test_example(request: pytest.FixtureRequest):
    fig = make_subplots()
    fig.add_trace(go.Scatter(x=[1, 2, 3, 4], y=[1, 2, 4, 8]))
    request.node.user_properties.append(fig)

Now, when running the test by invoking python -m pytest --html=report.html --self-contained-html . in the folder containing those two files, two new files are generated:

• my_plot.html
• report.html

Here is a screenshot of the plot itself, when opening my_plot.html:

And now, a screenshot of the test report, when opening report.html:

We can see that the plot is not rendered, even if present in the HTML file, as depicted in the following screenshot:

I'm not really sure why it is not rendered properly. I raised a question on StackOverflow and it seems that a solution exists, but I don't know how to integrate it properly.