Elements within "expandables" containers are not visible in ElementTree

[Asaurus1]

Checklist

• I have searched the existing issues for similar issues.
• I added a very descriptive title to this issue.
• I have provided sufficient information below to help reproduce this issue.

Summary

AppTest does not seem to capture elements created inside of expandables like st.status or st.expander. As mentioned in #7719, there's currently no public API for expander or status elements in AppTest but, even when accessed via AppTest.get('expandables')[0] there are no elements captured inside of the expandable element.

Reproducible Code Example

def test_status():
    from streamlit.testing.v1 import AppTest

    at = AppTest.from_string("import streamlit as st\nst.status().error('foo')")
    at.run()

    assert at.error[0].value == "foo"

also

def test_status():
    from streamlit.testing.v1 import AppTest

    at = AppTest.from_string("import streamlit as st\nst.expander().error('foo')")
    at.run()

    assert at.get('expandables')[0].error[0].value == "foo"

Steps To Reproduce

Run the function in streamlit 1.30.0+

Expected Behavior

Should behave like the following and raise no exception.

def test_status():
    from streamlit.testing.v1 import AppTest

    at = AppTest.from_string("import streamlit as st\nst.empty().error('foo')")
    at.run()

    assert at.error[0].value == "foo"

Current Behavior

IndexError on at.error[0]

Even if you change the final line to at.get('expandables')[0].error[0] you still get an IndexError on .error[0]. There doesn't seem to be any work-around for getting elements drawn inside expanders at the AppTest interface.

Is this a regression?

• Yes, this used to work in a previous version.

Debug info

• Streamlit version: 1.30.0
• Python version: 3.11.4
• Operating System: Independent
• Browser: N/A

Additional Information

No response

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[kajarenc]

thanks, @Asaurus1 for opening this issue!

@AnOctopus I think for the current version elements inside expendables are not reachable, and it is an expected behavior, is that correct?

[Asaurus1]

I'm going to close this as fixed --- it seems to work just fine if I actually write my tests properly, e.g.

def test_status():
    from streamlit.testing.v1 import AppTest

    at = AppTest.from_string("import streamlit as st\nst.status(label='WITH PROPER ARGUMENTS FOR THE FUNCTION CALLS').error('foo')")
    at.run()

    assert at.error[0].value == "foo"

[Asaurus1]

@AnOctopus Re-opening since I have determined a more specific bug. It seems that calling ".update()" on a status element clears it's contents. Parse_tree_from_messages probably just needs a a special case to handle these update messages without replacing the element entirely.

I'll update the first post when I'm back on a keyboard. I'm also not sure if #7923 fixes this or not, I will have to do some testing

To reproduce:

def test_status():
    from streamlit.testing.v1 import AppTest

    at = AppTest.from_string("import streamlit as st\nsts=st.status('bar')\nsts.error('foo')\nsts.update(state='complete')")
    at.run()

    assert at.error[0].value == "foo"

[Asaurus1]

It seems like #7923 does fix this.