🧪Unit vs Integration Testing
Stop arguing about whether something is a unit or integration test — get a sharp shared vocabulary, write the same feature at three test levels, and walk away with a written test strategy for a real service.
Phase 1Defining the Test Levels
Define unit, integration, and end-to-end without hand-waving
A unit test isn't about size — it's about isolation
6 minA unit test isn't about size — it's about isolation
Integration tests prove the wires connect
6 minIntegration tests prove the wires connect
End-to-end tests answer one question: does the user's path work?
6 minEnd-to-end tests answer one question: does the user's path work?
The test boundary is a design choice, not a discovery
7 minThe test boundary is a design choice, not a discovery
Phase 2The Same Feature at Three Levels
Write the same feature at three different test levels
Pick one feature and freeze it for the week
5 minPick one feature and freeze it for the week
The unit test: fast, focused, and lying about the world
6 minThe unit test: fast, focused, and lying about the world
The integration test: slower, sharper, and proves the seam
7 minThe integration test: slower, sharper, and proves the seam
The end-to-end test: slow, valuable, and used sparingly
7 minThe end-to-end test: slow, valuable, and used sparingly
Three tests, three trade-offs, one feature shipped with confidence
6 minThree tests, three trade-offs, one feature shipped with confidence
Phase 3Pyramids, Feedback Loops, and Flake
Connect the pyramid to feedback loops and flake
The integration suite that takes 40 minutes
7 minThe integration suite that takes 40 minutes
The flaky end-to-end test nobody can fix
7 minThe flaky end-to-end test nobody can fix
The PR that touches every test in the codebase
7 minThe PR that touches every test in the codebase
Choosing between coverage and confidence
7 minChoosing between coverage and confidence
Phase 4Plan a Real Test Strategy
Draft a real test strategy for a service you own
Write the test strategy for a service you actually ship
20 minWrite the test strategy for a service you actually ship
Frequently asked questions
- What's the actual difference between a unit test and an integration test?
- This is covered in the “Unit vs Integration Testing” learning path. Start with daily 5-minute micro-lessons that build from fundamentals to hands-on application.
- Should I mock the database in unit tests or use a real one?
- This is covered in the “Unit vs Integration Testing” learning path. Start with daily 5-minute micro-lessons that build from fundamentals to hands-on application.
- Why does the test pyramid say to write fewer end-to-end tests?
- This is covered in the “Unit vs Integration Testing” learning path. Start with daily 5-minute micro-lessons that build from fundamentals to hands-on application.
- How do I decide what level to test a feature at?
- This is covered in the “Unit vs Integration Testing” learning path. Start with daily 5-minute micro-lessons that build from fundamentals to hands-on application.
- What makes integration tests so flaky and how do I fix it?
- This is covered in the “Unit vs Integration Testing” learning path. Start with daily 5-minute micro-lessons that build from fundamentals to hands-on application.
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