Quarantine BlazorWebJsInitializersTest.InitializersRunsModernCallbacksByDefaultWhenPresent

[github-actions]

Failing Test(s)

Microsoft.AspNetCore.Components.E2ETests.ServerRenderingTests.BlazorWebJsInitializersTest.InitializersRunsModernCallbacksByDefaultWhenPresent

Error Message

OpenQA.Selenium.BrowserAssertFailedException : Xunit.Sdk.NotEmptyException: Assert.NotEmpty() Failure: Collection was empty
   at Xunit.Assert.NotEmpty(IEnumerable collection) in /_/src/xunit.assert/Asserts/CollectionAsserts.cs:line 539
   at Microsoft.AspNetCore.E2ETesting.WaitAssert.<>c__DisplayClass18_0.<Exists>b__0() in /mnt/vss/_work/1/s/src/Shared/E2ETesting/WaitAssert.cs:line 78
   at Microsoft.AspNetCore.E2ETesting.WaitAssert.<>c__DisplayClass21_0`1.<WaitAssertCore>b__0(IWebDriver _) in /mnt/vss/_work/1/s/src/Shared/E2ETesting/WaitAssert.cs:line 109
Screen shot captured at '/mnt/vss/_work/1/s/src/Components/test/E2ETest/bin/screenshots/182d6317a19a43bdb111ceec6c5d832b.png'
Encountered browser errors
[2026-04-10T14:13:35Z] [Warning] blazor.web.js: Initializer 'BasicTestApp.lib.module.js' will be ignored because multiple runtimes are available. Use 'before(Web|WebAssembly|Server)Start' and 'after(Web|WebAssembly|Server)Started' instead.
[2026-04-10T14:13:35Z] [Warning] blazor.web.js: Initializer 'JSInitializers/Classic/BasicTestApp.lib.module.js' will be ignored because multiple runtimes are available. Use 'before(Web|WebAssembly|Server)Start' and 'after(Web|WebAssembly|Server)Started' instead.

Stacktrace

Details

Xunit.Sdk.NotEmptyException: Assert.NotEmpty() Failure: Collection was empty
   at Xunit.Assert.NotEmpty(IEnumerable collection) in /_/src/xunit.assert/Asserts/CollectionAsserts.cs:line 539
   at Microsoft.AspNetCore.E2ETesting.WaitAssert.<>c__DisplayClass18_0.<Exists>b__0() in /mnt/vss/_work/1/s/src/Shared/E2ETesting/WaitAssert.cs:line 78
   at Microsoft.AspNetCore.E2ETesting.WaitAssert.<>c__DisplayClass21_0`1.<WaitAssertCore>b__0(IWebDriver _) in /mnt/vss/_work/1/s/src/Shared/E2ETesting/WaitAssert.cs:line 109
   at OpenQA.Selenium.Support.UI.DefaultWait`1.Until[TResult](Func`2 condition)
   at Microsoft.AspNetCore.E2ETesting.WaitAssert.WaitAssertCore[TResult](IWebDriver driver, Func`1 func, TimeSpan timeout, String userMessage) in /mnt/vss/_work/1/s/src/Shared/E2ETesting/WaitAssert.cs:line 120
   at Microsoft.AspNetCore.E2ETesting.WaitAssert.Exists(IWebDriver driver, By finder, TimeSpan timeout, String userMessage) in /mnt/vss/_work/1/s/src/Shared/E2ETesting/WaitAssert.cs:line 78
   at Microsoft.AspNetCore.Components.E2ETests.ServerRenderingTests.BlazorWebJsInitializersTest.InitializersRunsModernCallbacksByDefaultWhenPresent(Boolean streaming, Boolean webassembly, Boolean server, String[] expectedInvokedCallbacks) in /mnt/vss/_work/1/s/src/Components/test/E2ETest/ServerRenderingTests/BlazorWebJsInitializersTest.cs

Logs

Details

The test InitializersRunsModernCallbacksByDefaultWhenPresent navigates to an /initializers page that renders JS initializer callbacks as DOM elements. The test asserts that specific callback elements exist in the DOM (e.g., classic-and-modern-before-web-start, classic-and-modern-after-web-started, etc.). When the test fails, the collection is empty — meaning the expected DOM elements were never rendered, suggesting the JavaScript initializers were not invoked.

Browser console warnings indicate the classic-style initializers were being ignored in favor of modern-style callbacks, but the modern callbacks also failed to render their output in time.

Build

https://dev.azure.com/dnceng-public/public/_build/results?buildId=1373948

Note

🔒 Integrity filter blocked 6 items

The following items were blocked because they don't meet the GitHub integrity level.

• #66003 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #66084 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #66228 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #66276 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #65696 search_pull_requests: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #65696 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".

To allow these resources, lower min-integrity in your GitHub frontmatter:

tools:
  github:
    min-integrity: approved  # merged | approved | unapproved | none

Generated by Daily Test Quarantine Management · ● 4.9M · ◷

[github-actions]

Investigation

The test InitializersRunsModernCallbacksByDefaultWhenPresent is a Selenium-based E2E test that validates Blazor's JavaScript initializer pipeline. It:

1. Navigates to /initializers?streaming={...}&wasm={...}&server={...}
2. Asserts that specific callback marker DOM elements appear (e.g., #classic-and-modern-before-web-start)
3. Asserts the count of rendered paragraphs matches the expected callbacks list

Failure pattern: The test fails with Assert.NotEmpty() Failure: Collection was empty — the Browser.Exists(By.Id(callback)) call times out because the callback element never appears in the DOM.

Browser console warnings in the failure log:

Initializer 'BasicTestApp.lib.module.js' will be ignored because multiple runtimes are available.
Use 'before(Web|WebAssembly|Server)Start' and 'after(Web|WebAssembly|Server)Started' instead.

This suggests the classic-style .lib.module.js initializers are being silently dropped when multiple runtimes (WebAssembly + Server) are available. The test's InitializerTestData includes test cases with both webassembly: True and server: True, which would trigger this multi-runtime path.

Root cause hypothesis: This appears to be a race condition or a regression in the initializer dispatch logic when multiple Blazor runtimes are present. When the classic initializers are ignored due to multiple runtimes being present, the modern callbacks may also not be firing their DOM marker elements in time (or at all), causing the WaitAssert.Exists to time out.

Frequency: The test has failed 23+ times on the main branch over the past 30 days, confirming this is a consistent flaky failure rather than a one-off issue.

Suggested investigation:

• Check recent changes to blazor.web.js initializer dispatch logic (discoverWebAssemblyOptions, initializersModule)
• Review how InitializerTestData with both webassembly: True, server: True exercises the multi-runtime path
• Verify whether the DOM marker elements are rendered by the JS initializer callbacks themselves or by server-side logic

Cannot determine an obvious quick fix at this time. The test is being quarantined to unblock CI while the root cause is investigated.

Note

🔒 Integrity filter blocked 6 items

The following items were blocked because they don't meet the GitHub integrity level.

• #66003 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #66084 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #66228 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #66276 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #65696 search_pull_requests: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
• #65696 pull_request_read: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".

To allow these resources, lower min-integrity in your GitHub frontmatter:

tools:
  github:
    min-integrity: approved  # merged | approved | unapproved | none

Generated by Daily Test Quarantine Management · ● 4.9M · ◷

[javiercn]

Don't think it was a flaky test issue, but a real issue that I believe has been fixed.