test: this test if stacktraces are cleared in output widgets

Depends on jupyter-server/jupyter_server#326

share/jupyter/voila/templates/base/static/main.js

@@ -6,6 +6,28 @@
 * The full license is in the file LICENSE, distributed with this software. *
 ****************************************************************************/
 
+window.VoilaDebug = VoilaDebug = {
+    _widgetManagerPromiseResolve: null,
+    _widgetManagerPromise: null,
+    async waitForWidgetManager() {
+        await _widgetManagerPromise;
+    },
+    async waitForViews(modelId) {
+        const widgetManager = await window.VoilaDebug._widgetManagerPromise;
+        const model = await widgetManager._models[modelId];
+        await Promise.all(Object.values(model.views))
+    },
+    async waitForAllViews() {
+        console.log(window.VoilaDebug._widgetManagerPromise)
+        const widgetManager = await window.VoilaDebug._widgetManagerPromise;
+        for(const modelId in widgetManager._models) {
+            await VoilaDebug.waitForViews(modelId);
+        }
+    }
+}
+
+window.VoilaDebug._widgetManagerPromise = new Promise((resolve) => window.VoilaDebug._widgetManagerPromiseResolve = resolve),
+
 // NOTE: this file is not transpiled, async/await is the only modern feature we use here
 require([window.voila_js_url || 'static/voila'], function(voila) {
     // requirejs doesn't like to be passed an async function, so create one inside
@@ -45,6 +67,7 @@ require([window.voila_js_url || 'static/voila'], function(voila) {
             });
             await widgetManager.build_widgets();
             voila.renderMathJax();
+            window.VoilaDebug._widgetManagerPromiseResolve(widgetManager);
         }
 
         if (document.readyState === 'complete') {

tests/app/show_traceback_test.py

@@ -1,4 +1,8 @@
+import asyncio
+import os
+
 import pytest
+import pyppeteer
 
 
 @pytest.fixture(params=[True, False])
@@ -21,3 +25,45 @@ async def test_syntax_error(http_server_client, syntax_error_notebook_url, show_
     else:
         assert 'There was an error when executing cell' in output
         assert 'This should not be executed' not in output
+
+
+async def test_output_widget_traceback(http_server_client, exception_runtime_notebook_url, show_tracebacks):
+    options = dict(headless=False, devtools=True) if os.environ.get('VOILA_TEST_DEBUG_VISUAL', False) else {}
+    # with headless and gpu enabled, we get slightly different results on the same OS
+    # we can enable it if we need to, since we allow for a tolerance
+    launcher = pyppeteer.launcher.Launcher(options=options, autoClose=False, args=['--font-render-hinting=none', '--disable-gpu'])
+    browser = await launcher.launch()
+    page = await browser.newPage()
+    try:
+        await page.goto(http_server_client.get_url(exception_runtime_notebook_url), waitUntil='networkidle2')
+        await page.evaluate('async () => await VoilaDebug.widgetManagerPromise')
+        await page.evaluate('async () => await VoilaDebug.waitForAllViews()')
+        await page.evaluate("document.querySelector('.button2').click()")
+        for i in range(20):
+            await asyncio.sleep(0.05)
+            output_text = await page.evaluate("document.querySelector('.output_exception').innerText")
+            if output_text:
+                break
+        else:
+            assert False, f"Never received output"
+        if show_tracebacks:
+            assert 'this happens after the notebook is executed' in output_text
+        else:
+            assert 'this happens after the notebook is executed' not in output_text
+    except Exception as e:  # noqa
+        if os.environ.get('VOILA_TEST_DEBUG_VISUAL', False):
+            import traceback
+            traceback.print_exc()
+            # may want to add --async-test-timeout=60 to pytest arguments
+            print("Waiting for 60 second for visual inspection (hit ctrl-c to break)")
+            import sys
+            sys.stdout.flush()
+            sys.stderr.flush()
+            try:
+                await asyncio.sleep(60)
+            except:  # noqa ignore ctrl-c
+                pass
+        raise e
+    finally:
+        await browser.close()
+        await launcher.killChrome()

tests/conftest.py

@@ -22,6 +22,18 @@ def syntax_error_notebook_url(base_url):
     return base_url + "voila/render/syntax_error.ipynb"
 
 
+@pytest.fixture
+def exception_runtime_notebook_url(base_url):
+    return base_url + "voila/render/exception_runtime.ipynb"
+
+
 @pytest.fixture
 def voila_notebook(notebook_directory):
     return os.path.join(notebook_directory, 'print.ipynb')
+
+
+# this forces the event_loop fixture in pytest_asyncio to use the same ioloop as pytest_tornasync
+@pytest.fixture()
+def event_loop(io_loop):
+    import asyncio
+    return asyncio.get_event_loop()

voila/app.py

@@ -413,6 +413,8 @@ def start(self):
             parent=self,
             connection_dir=self.connection_dir,
             kernel_spec_manager=self.kernel_spec_manager,
+            allow_tracebacks=self.voila_configuration.show_tracebacks,
+            traceback_replacement_message='An error occurred, run Voilà with --show_traceback=True or --debug to show the traceback.',
             allowed_message_types=[
                 'comm_open',
                 'comm_close',