closes #1053 - add test for complex callback graph with preventDefault

tests/integration/callbacks/test_multiple_callbacks.py

@@ -2,8 +2,10 @@
 from multiprocessing import Value
 
 import dash_html_components as html
+import dash_core_components as dcc
 import dash
 from dash.dependencies import Input, Output
+from dash.exceptions import PreventUpdate
 
 
 def test_cbmt001_called_multiple_times_and_out_of_order(dash_duo):
@@ -36,3 +38,37 @@ def update_output(n_clicks):
     dash_duo.percy_snapshot(
         name="test_callbacks_called_multiple_times_and_out_of_order"
     )
+
+
+def test_cbmt002_canceled_intermediate_callback(dash_duo):
+    # see https://github.com/plotly/dash/issues/1053
+    app = dash.Dash(__name__)
+    app.layout = html.Div([
+        dcc.Input(id='a', value="x"),
+        html.Div('b', id='b'),
+        html.Div('c', id='c'),
+        html.Div(id='out')
+    ])
+
+    @app.callback(
+        Output("out", "children"),
+        [Input("a", "value"), Input("b", "children"), Input("c", "children")]
+    )
+    def set_out(a, b, c):
+        return "{}/{}/{}".format(a, b, c)
+
+    @app.callback(Output("b", "children"), [Input("a", "value")])
+    def set_b(a):
+        raise PreventUpdate
+
+    @app.callback(Output("c", "children"), [Input("a", "value")])
+    def set_c(a):
+        return a
+
+    dash_duo.start_server(app)
+    dash_duo.wait_for_text_to_equal("#out", "x/b/x")
+    chars = "x"
+    for i in list(range(10)) * 2:
+        dash_duo.find_element("#a").send_keys(str(i))
+        chars += str(i)
+        dash_duo.wait_for_text_to_equal("#out", "{0}/b/{0}".format(chars))