Check Upstream Flake Agent Skill

Check Upstream Flake

Check if a failing test is a known upstream flake in the Chromium LUCI Analysis

database. This queries the REST API at analysis.api.luci.app to retrieve

historical pass/fail/flake data for a test in the Chromium CI infrastructure.

When to Use

• Investigating intermittent test failures before deciding on a fix approach
• Evaluating test disable PRs to verify upstream flakiness claims
• During PR review (via the review skill) when assessing test filter changes
• Working on "pending" stories that involve Chromium test failures

The Job

When invoked with a test name:

• Search for matching test IDs in the Chromium LUCI Analysis database
• Retrieve flakiness statistics for each match over the lookback period
• Analyze pass/fail/flake rates
• Report a verdict and recommendation

Usage

# Basic: check a specific test (default 30-day lookback)
python3 ./script/check-upstream-flake.py "WebUIURLLoaderFactoryTest.RangeRequest"

# Longer lookback window
python3 ./script/check-upstream-flake.py "WebUIURLLoaderFactoryTest.RangeRequest" --days 60

# JSON output (for programmatic use)
python3 ./script/check-upstream-flake.py "WebUIURLLoaderFactoryTest.RangeRequest" --json

# Search by test class name (finds all methods)
python3 ./script/check-upstream-flake.py "WebUIURLLoaderFactoryTest"

Arguments:

• test_name (required): Test name or substring to search for
• --days N: Lookback window in days (default: 30, max: 90)
• --json: Output JSON instead of markdown

Exit codes:

• 0: Success (results found and reported)
• 1: Error (network, API, etc.)
• 2: No matching test IDs found

Interpreting Results

The script produces one of five verdicts:

| Verdict | Flake Rate | Action |

| -------------------------------- | ------------------ | ------------------------------------------------------------------------------------------------------------------------ |

| Known upstream flake | >= 5% | Safe to add to filter file. Document upstream flakiness in the filter comment. |

| Occasional upstream failures | 1-5% | Consider filtering. Document findings. May still warrant investigation. |

| Stable upstream | < 1% | Investigate Brave-specific causes. The test is stable in Chromium, so Brave code changes are likely causing the failure. |

| Insufficient data | N/A (<10 verdicts) | Cannot determine from upstream data. Manual investigation needed. |

| Not found | N/A | Test not in Chromium database. May be Brave-specific or use a different ID format. |

Flake rate is calculated as (failed + flaky) / (passed + failed + flaky).

Skipped and precluded verdicts are excluded from the rate.

How Results Inform Decisions

Known upstream flake or occasional failures

• Disabling via filter file is appropriate
• Use the most specific filter file possible (platform/sanitizer-specific)
• Include in the filter comment: "Known upstream flake (X% flake rate over N

days per LUCI Analysis)"

• Reference this in commit message and PR body

Stable upstream

• The test passes reliably in Chromium CI
• Focus investigation on Brave-specific factors:
• Check brave/chromium_src/ overrides in related directories
• Look for Brave features that change timing or behavior
• Check if Brave adds UI elements that affect the test
• A filter disable should be a last resort and needs strong justification

Not found or insufficient data

• The test may use a different ID format in LUCI
• Try searching with just the class name or a broader substring
• Check manually at https://ci.chromium.org/ui/p/chromium/test-search
• Proceed with normal investigation

API Details

The script uses the LUCI Analysis REST API (pRPC protocol):

• QueryTests:

POST https://analysis.api.luci.app/prpc/luci.analysis.v1.TestHistory/QueryTests

• QueryStats:

POST https://analysis.api.luci.app/prpc/luci.analysis.v1.TestHistory/QueryStats

• Query (fallback):

POST https://analysis.api.luci.app/prpc/luci.analysis.v1.TestHistory/Query

No authentication is required for public Chromium data.

Test IDs in LUCI follow the format:

ninja://{gn_path}:{target}/{TestSuite}.{TestMethod}

Limitations

• Only covers Chromium upstream data (not Brave CI)
• Test ID format may not match for all tests
• Historical data limited to ~90 days
• Does not compare failure logs/output (only counts pass/fail/flake)
• Cannot distinguish between different failure modes for the same test