Famous article and talk by J. Rainsburger http://blog.thecodewhisperer.com/permalink/integrated-tests-are-a-scam
Gary Bernhardt (from destroyallsoftware.com) has also created several good screencasts on isolated testing.
- https://www.destroyallsoftware.com/screencasts/catalog/clarity-via-isolated-tests
- https://www.destroyallsoftware.com/screencasts/catalog/isolating-by-separating-value
- https://www.destroyallsoftware.com/screencasts/catalog/a-magical-isolation-story
- https://www.destroyallsoftware.com/screencasts/catalog/test-isolation-without-mocks
- https://www.destroyallsoftware.com/screencasts/catalog/web-apps-when-to-test-in-isolation
Good article here too https://www.destroyallsoftware.com/blog/2014/test-isolation-is-about-avoiding-mocks
See also:
- https://www.obeythetestinggoat.com/book/chapter_purist_unit_tests.html
- https://github.com/testdouble/contributing-tests/wiki/London-school-TDD (a general wiki on interesting testing topics)