Testing and Validation (pyATS, Batfish)

Automation without testing is dangerous — you can misconfigure thousands of devices as quickly as one. This lesson covers testing and validation tools that ensure your automation changes are correct before they are deployed and verified after deployment.

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Why Test Network Automation?

Risk	Consequence
Untested config push	Outage affecting thousands of users
Typo in a template	Wrong IP address, broken routing
Missing rollback plan	Cannot recover from a failed change
No pre-change validation	Deploy a change that conflicts with existing config
No post-change validation	Assume the change worked without verification

The Testing Pyramid for Network Automation

          ┌─────────────┐
          │  Integration │   Test against real/virtual devices
          │    Tests     │   (pyATS, robot framework)
          ├─────────────┤
          │  Simulation  │   Model the network and analyse
          │    Tests     │   (Batfish, GNS3)
          ├─────────────┤
          │    Unit      │   Test templates, data, logic
          │    Tests     │   (pytest, yamllint, j2lint)
          └─────────────┘

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Unit Testing

Linting Data Files

# Validate YAML syntax
pip install yamllint
yamllint host_vars/

# Validate Jinja2 templates
pip install j2lint
j2lint templates/