flaky-test-detector

Testing & Quality

Detect flaky tests by scanning recent AzDo CI builds for test failures recurring across multiple unrelated PRs. Use when investigating intermittent failures, CI instability, deciding which tests to quarantine, or checking if RunTestCasesInSequence no-ops are causing parallel-safety issues.

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Flaky Test Detector

Identifies tests that fail intermittently across unrelated PRs — a strong signal of flakiness rather than a genuine regression. Also cross-references with existing fix PRs.

When to Use

Investigating CI instability ("is this test failure my fault or flaky?")
Periodic hygiene: finding tests to quarantine or fix
Before marking a test as Skip = "Flaky" — confirm it actually is flaky
Checking if RunTestCasesInSequence (a no-op in xUnit 2) is masking parallelism bugs

How It Works

Queries Azure DevOps builds API directly for recent failed fsharp-ci PR builds
Extracts test failures from each build via Get-BuildErrors.ps1
Aggregates by test name across distinct PRs
Cross-references with GitHub PRs that may address the flaky tests
Tests failing in 3+ distinct PRs are flagged as flaky

Usage

Quick scan (last 14 days, 50 builds, threshold = 3)

pwsh .github/skills/flaky-test-detector/scripts/Get-FlakyTests.ps1

Custom parameters

# More aggressive: 2+ PRs over 7 days
pwsh .github/skills/flaky-test-detector/scripts/Get-FlakyTests.ps1 -MinPRFailures 2 -DaysBack 7

# Wider net: 100 builds over 30 days  
pwsh .github/skills/flaky-test-detector/scripts/Get-FlakyTests.ps1 -MaxBuilds 100 -DaysBack 30

Parameters

Parameter	Default	Description
`-MaxBuilds`	50	Maximum number of failed builds to scan from AzDo
`-MinPRFailures`	3	Min distinct PRs a test must fail in to be flagged
`-DaysBack`	14	Only consider builds within this time window
`-DefinitionId`	90	AzDo pipeline definition ID (90 = fsharp-ci)
`-Org`	dnceng-public	Azure DevOps organization
`-Project`	public	Azure DevOps project

Output

The script produces:

Console report with ranked flaky tests, PR numbers, job names, and sample errors
Structured objects (PowerShell) for programmatic consumption

Interpreting Results

DistinctPRs ≥ 5: Almost certainly flaky — consider quarantining immediately
DistinctPRs = 3–4: Likely flaky — investigate root cause
DistinctPRs = 2: Possibly flaky or a shared dependency issue — monitor

Follow-up Actions

After identifying a flaky test:

Check if there's already a GitHub issue for it
If not, file one with the Area-flaky-test label
Consider marking with [<Fact(Skip = "Flaky: #ISSUE")>] if it blocks CI
Fix the root cause (timing, file locking, thread safety, etc.)