adding test for custom dash server

BSd3v · BSd3v · commit f7331d3f7e97 · 2025-09-17T12:31:35.000-04:00
diff --git a/tests/backend_tests/test_custom_backend.py b/tests/backend_tests/test_custom_backend.py
@@ -0,0 +1,243 @@
+import pytest
+from dash import Dash, Input, Output, html, dcc
+from fastapi import FastAPI
+import traceback
+import re
+from dash.backends._fastapi import FastAPIDashServer
+
+
+class CustomDashServer(FastAPIDashServer):
+    def _get_traceback(self, _secret, error: Exception):
+        tb = error.__traceback__
+        errors = traceback.format_exception(type(error), error, tb)
+        pass_errs = []
+        callback_handled = False
+        for err in errors:
+            if self.error_handling_mode == "prune":
+                if not callback_handled:
+                    if "callback invoked" in str(err) and "_callback.py" in str(err):
+                        callback_handled = True
+                    continue
+            pass_errs.append(err)
+        formatted_tb = "".join(pass_errs)
+        error_type = type(error).__name__
+        error_msg = str(error)
+        # Parse traceback lines to group by file
+        file_cards = []
+        pattern = re.compile(r'  File "(.+)", line (\d+), in (\w+)')
+        lines = formatted_tb.split("\n")
+        current_file = None
+        card_lines = []
+        for line in lines[:-1]:  # Skip the last line (error message)
+            match = pattern.match(line)
+            if match:
+                if current_file and card_lines:
+                    file_cards.append((current_file, card_lines))
+                current_file = (
+                    f"{match.group(1)} (line {match.group(2)}, in {match.group(3)})"
+                )
+                card_lines = [line]
+            elif current_file:
+                card_lines.append(line)
+        if current_file and card_lines:
+            file_cards.append((current_file, card_lines))
+        cards_html = ""
+        for filename, card in file_cards:
+            cards_html += (
+                f"""
+            <div class=\"error-card\">
+                <div class=\"error-card-header\">{filename}</div>
+                <pre class=\"error-card-traceback\">"""
+                + "\n".join(card)
+                + """</pre>
+            </div>
+            """
+            )
+        html = f"""
+        <!doctype html>
+        <html lang=\"en\">
+          <head>
+            <title>{error_type}: {error_msg} // Custom Debugger</title>
+            <style>
+              body {{ font-family: monospace; background: #fff; color: #333; }}
+              .debugger {{ margin: 2em; max-width: 700px; }}
+            </style>
+          </head>
+          <body>
+            <div class=\"debugger\">
+              <h1>{error_type}: {error_msg}</h1>
+              {cards_html}
+            </div>
+          </body>
+        </html>
+        """
+        return html
+
+
+@pytest.mark.parametrize(
+    "fixture,input_value",
+    [
+        ("dash_duo", "Hello CustomBackend!"),
+    ],
+)
+def test_custom_backend_basic_callback(request, fixture, input_value):
+    dash_duo = request.getfixturevalue(fixture)
+    app = Dash(__name__, backend=CustomDashServer)
+    app.layout = html.Div(
+        [dcc.Input(id="input", value=input_value, type="text"), html.Div(id="output")]
+    )
+
+    @app.callback(Output("output", "children"), Input("input", "value"))
+    def update_output(value):
+        return f"You typed: {value}"
+
+    dash_duo.start_server(app)
+    dash_duo.wait_for_text_to_equal("#output", f"You typed: {input_value}")
+    dash_duo.clear_input(dash_duo.find_element("#input"))
+    dash_duo.find_element("#input").send_keys("CustomBackend Test")
+    dash_duo.wait_for_text_to_equal("#output", "You typed: CustomBackend Test")
+    assert dash_duo.get_logs() == []
+
+
+@pytest.mark.parametrize(
+    "fixture,start_server_kwargs",
+    [
+        ("dash_duo", {"debug": True, "reload": False, "dev_tools_ui": True}),
+    ],
+)
+def test_custom_backend_error_handling(request, fixture, start_server_kwargs):
+    dash_duo = request.getfixturevalue(fixture)
+    app = Dash(__name__, backend=CustomDashServer)
+    app.layout = html.Div(
+        [html.Button(id="btn", children="Error", n_clicks=0), html.Div(id="output")]
+    )
+
+    @app.callback(Output("output", "children"), Input("btn", "n_clicks"))
+    def error_callback(n):
+        if n and n > 0:
+            return 1 / 0  # Intentional error
+        return "No error"
+
+    dash_duo.start_server(app, **start_server_kwargs)
+    dash_duo.wait_for_text_to_equal("#output", "No error")
+    dash_duo.find_element("#btn").click()
+    dash_duo.wait_for_text_to_equal(dash_duo.devtools_error_count_locator, "1")
+
+
+def get_error_html(dash_duo, index):
+    # error is in an iframe so is annoying to read out - get it from the store
+    return dash_duo.driver.execute_script(
+        "return store.getState().error.backEnd[{}].error.html;".format(index)
+    )
+
+
+@pytest.mark.parametrize(
+    "fixture,start_server_kwargs",
+    [
+        (
+            "dash_duo",
+            {
+                "debug": True,
+                "dev_tools_ui": True,
+                "dev_tools_prune_errors": False,
+                "reload": False,
+            },
+        ),
+    ],
+)
+def test_custom_backend_error_handling_no_prune(request, fixture, start_server_kwargs):
+    dash_duo = request.getfixturevalue(fixture)
+    app = Dash(__name__, backend=CustomDashServer)
+    app.layout = html.Div(
+        [html.Button(id="btn", children="Error", n_clicks=0), html.Div(id="output")]
+    )
+
+    @app.callback(Output("output", "children"), Input("btn", "n_clicks"))
+    def error_callback(n):
+        if n and n > 0:
+            return 1 / 0  # Intentional error
+        return "No error"
+
+    dash_duo.start_server(app, **start_server_kwargs)
+    dash_duo.wait_for_text_to_equal("#output", "No error")
+    dash_duo.find_element("#btn").click()
+    dash_duo.wait_for_text_to_equal(dash_duo.devtools_error_count_locator, "1")
+
+    error0 = get_error_html(dash_duo, 0)
+    assert "Custom Debugger" in error0
+    assert "in error_callback" in error0
+    assert "ZeroDivisionError" in error0
+    assert "_callback.py" in error0
+
+
+@pytest.mark.parametrize(
+    "fixture,start_server_kwargs, error_msg",
+    [
+        ("dash_duo", {"debug": True, "reload": False}, "custombackend.py"),
+    ],
+)
+def test_custom_backend_error_handling_prune(
+    request, fixture, start_server_kwargs, error_msg
+):
+    dash_duo = request.getfixturevalue(fixture)
+    app = Dash(__name__, backend=CustomDashServer)
+    app.layout = html.Div(
+        [html.Button(id="btn", children="Error", n_clicks=0), html.Div(id="output")]
+    )
+
+    @app.callback(Output("output", "children"), Input("btn", "n_clicks"))
+    def error_callback(n):
+        if n and n > 0:
+            return 1 / 0  # Intentional error
+        return "No error"
+
+    dash_duo.start_server(app, **start_server_kwargs)
+    dash_duo.wait_for_text_to_equal("#output", "No error")
+    dash_duo.find_element("#btn").click()
+    dash_duo.wait_for_text_to_equal(dash_duo.devtools_error_count_locator, "1")
+
+    error0 = get_error_html(dash_duo, 0)
+    assert "Custom Debugger" in error0
+    assert "in error_callback" in error0
+    assert "ZeroDivisionError" in error0
+    assert "_callback.py" not in error0
+
+
+@pytest.mark.parametrize(
+    "fixture,input_value",
+    [
+        ("dash_duo", "Background CustomBackend!"),
+    ],
+)
+def test_custom_backend_background_callback(request, fixture, input_value):
+    dash_duo = request.getfixturevalue(fixture)
+    import diskcache
+
+    cache = diskcache.Cache("./cache")
+    from dash.background_callback import DiskcacheManager
+
+    background_callback_manager = DiskcacheManager(cache)
+
+    app = Dash(
+        __name__,
+        backend=CustomDashServer,
+        background_callback_manager=background_callback_manager,
+    )
+    app.layout = html.Div(
+        [dcc.Input(id="input", value=input_value, type="text"), html.Div(id="output")]
+    )
+
+    @app.callback(
+        Output("output", "children"), Input("input", "value"), background=True
+    )
+    def update_output_bg(value):
+        return f"Background typed: {value}"
+
+    dash_duo.start_server(app)
+    dash_duo.wait_for_text_to_equal("#output", f"Background typed: {input_value}")
+    dash_duo.clear_input(dash_duo.find_element("#input"))
+    dash_duo.find_element("#input").send_keys("CustomBackend BG Test")
+    dash_duo.wait_for_text_to_equal(
+        "#output", "Background typed: CustomBackend BG Test"
+    )
+    assert dash_duo.get_logs() == []
