adding test and docstring

Author: BSd3v

dash/_callback.py

@@ -167,6 +167,14 @@ def callback(
             Mark all dependencies as not required on the initial layout checks.
         :param hidden:
             Hide the callback from the devtools callbacks tab.
+        :param api_endpoint:
+            If provided, the callback will be available at the given API endpoint.
+            This allows you to call the callback directly through HTTP requests
+            instead of through the Dash front-end. The endpoint should be a string
+            that starts with a forward slash (e.g. `/my_callback`).
+            The endpoint is relative to the Dash app's base URL.
+            Note that the endpoint will not appear in the list of registered
+            callbacks in the Dash devtools.
     """
 
     background_spec = None

tests/integration/callbacks/test_api_callback.py

@@ -0,0 +1,53 @@
+
+from dash import (
+    Dash,
+    Input,
+    Output,
+    html,
+    ctx,
+)
+import requests
+import json
+from flask import jsonify
+
+test_string = ('{"step_0": "Data fetched - 1", "step_1": "Data fetched - 1", "step_2": "Data fetched - 1", '
+               '"step_3": "Data fetched - 1", "step_4": "Data fetched - 1"}')
+
+def test_apib001_api_callback(dash_duo):
+
+    app = Dash(__name__)
+    app.layout = html.Div([
+        html.Button("Slow Callback", id="slow-btn"),
+        html.Div(id="slow-output"),
+    ])
+
+    def get_data(n_clicks):
+        # Simulate an async data fetch
+        return f"Data fetched - {n_clicks}"
+
+    @app.callback(
+        Output("slow-output", "children"),
+        Input("slow-btn", "n_clicks"),
+        prevent_initial_call=True,
+        api_endpoint='/api/slow_callback',  # Example API path for the slow callback
+    )
+    def slow_callback(n_clicks):
+        data = {}
+        for i in range(5):
+            data[f'step_{i}'] = get_data(n_clicks)
+        ret = f"{json.dumps(data)}"
+        if ctx:
+            return ret
+        return jsonify(ret)
+
+    app.setup_apis()
+
+    dash_duo.start_server(app)
+
+    dash_duo.wait_for_element("#slow-btn").click()
+    dash_duo.wait_for_text_to_equal("#slow-output", test_string)
+    r = requests.post(dash_duo.server_url +'/api/slow_callback',
+                  json={'n_clicks': 1},
+                  headers={'Content-Type': 'application/json'})
+    assert r.status_code == 200
+    assert r.json() == test_string