Testing Data Applications

Data pipelines are notoriously hard to test. The data changes, external systems are unreliable, and transformations can be complex. But untested pipelines break silently — producing wrong data that spreads downstream before anyone notices. This lesson covers testing strategies, fixtures, snapshot testing, and CI/CD for data applications.

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Why Test Data Pipelines?

Untested Pipeline                  Tested Pipeline
┌─────────────────────┐           ┌─────────────────────┐
│ "It worked last     │           │ Unit tests catch     │
│  time I ran it"     │           │ logic bugs early     │
│                     │           │                      │
│ Fails silently      │           │ Integration tests    │
│ Wrong data loaded   │           │ catch system issues  │
│ Nobody notices for  │           │                      │
│ days or weeks       │           │ CI/CD prevents bad   │
│                     │           │ code from deploying  │
└─────────────────────┘           └─────────────────────┘

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Testing Layers