Unit test vs. Integration test

https://twitter.com/codejobs/status/813056723271450624

Still confused about the difference between a unit test and and integration test?

Both are important tiers of the test pyramid.

Unit tests

• Run fast! We are talking ms here
• Test your code in isolation
• Mock external dependencies
• Avoid database access, network requests, and the file system
• Be able to run in parallel
• Allow you to practice TDD (if you want)

Integration tests

• Run reasonably fast. Anywhere from a few seconds to a minute
• Test how your code interacts with the framework
• May or may not mock external dependencies
• May access a local database or filesystem or network
• May or may not run in parallel
• Should NOT be used to practice TDD

Even a few seconds is too slow to get the rapid feedback required for TDD.

Integration tests are a nice second layer of defense that should be run regularly for example on a CI server. They can catch issues that might have been missed in the unit tests and offer a more realistic test environment.