Blame Mode for Test Debugging

Blame mode helps identify tests that cause crashes, hangs, or process termination. It sequences test execution and logs which test was running when a failure occurred.

When to Use Blame Mode

• Tests crash the test host process
• Tests hang indefinitely
• Debugging intermittent test failures
• Identifying tests that corrupt shared state
• CI pipelines fail mysteriously

Basic Blame Mode

Enable blame mode to log test sequence and identify the last running test:

dotnet test --blame

Output: Creates a Sequence.xml file in TestResults/ showing test execution order.

Crash Dump Collection

Collect crash dumps when tests crash the host process:

# Collect crash dump on failure
dotnet test --blame-crash

# Specify dump type (mini or full)
dotnet test --blame-crash --blame-crash-dump-type mini
dotnet test --blame-crash --blame-crash-dump-type full

# Collect dump on unexpected exit
dotnet test --blame-crash-collect-always

Dump Types

Recommendation: Start with mini dumps. Use full only when mini dumps lack sufficient detail.

Hang Detection

Detect and collect information when tests hang:

# Detect hangs with timeout
dotnet test --blame-hang --blame-hang-timeout 5m

# Specify dump type for hangs
dotnet test --blame-hang --blame-hang-dump-type mini --blame-hang-timeout 3m

Timeout Format

• 5m - 5 minutes
• 30s - 30 seconds
• 1h - 1 hour
• 5000ms - 5000 milliseconds

Combined Usage

For comprehensive debugging, combine options:

dotnet test \\
  --blame \\
  --blame-crash \\
  --blame-crash-dump-type mini \\
  --blame-hang \\
  --blame-hang-timeout 5m \\
  --blame-hang-dump-type mini

Results Location

Blame data is saved to:

TestResults/
├── {guid}/
│   ├── Sequence.xml          # Test execution sequence
│   ├── crash_dump.dmp        # Crash dump (if crash occurred)
│   └── hang_dump.dmp         # Hang dump (if timeout occurred)

Specify custom location:

dotnet test --blame --results-directory ./MyResults

Analyzing Results

Reading Sequence.xml

The sequence file shows tests in execution order:

Analyzing Dumps

Use Visual Studio or WinDbg to analyze .dmp files:

# Windows: Open in Visual Studio
# Linux/Mac: Use lldb or dotnet-dump
dotnet-dump analyze crash_dump.dmp

CI/CD Integration

For CI pipelines, enable blame mode to diagnose failures:

dotnet test \\
  --blame \\
  --blame-crash \\
  --blame-hang --blame-hang-timeout 10m \\
  --logger trx \\
  --results-directory ./TestResults

Artifacts to preserve:

• TestResults/ directory
• Any .dmp files
• Sequence.xml files

Common Scenarios

Scenario: Random test failures in CI

dotnet test --blame --blame-crash

Check Sequence.xml to find which test was running during failure.

Scenario: Tests hang indefinitely

dotnet test --blame-hang --blame-hang-timeout 5m --blame-hang-dump-type full

Analyze the hang dump to find deadlocks or infinite loops.

Scenario: Test host crashes with no output

dotnet test --blame-crash --blame-crash-dump-type full --blame-crash-collect-always

Use full dump to get complete memory state for analysis.