Function test_init_app_with_flask_run_pattern

tests/unit/test_configs.py:529–548

Test that init_app works correctly with the flask run pattern. This tests the fix for https://github.com/plotly/dash/issues/3787 where using flask run would cause a ValueError about duplicate blueprint registration because init_app was called twice (once automatically in __init__ wi

()

def test_init_app_with_flask_run_pattern():
    """Test that init_app works correctly with the flask run pattern.

    This tests the fix for https://github.com/plotly/dash/issues/3787
    where using flask run would cause a ValueError about duplicate blueprint
    registration because init_app was called twice (once automatically in
    __init__ with server=True, and once by the user in their create_app factory).
    """
    # Simulate the flask run pattern where:
    # 1. Dash app is created with server=True (default)
    # 2. User's create_app factory calls init_app with their Flask server
    external_server = Flask("external_test")
    app = Dash(__name__)

    # This should NOT raise "ValueError: The name '_dash_assets' is already registered"
    app.init_app(external_server)

    # Verify the backend now uses the external server
    assert app.server is external_server
    assert app.backend.server is external_server


def test_init_app_server_false_pattern():