In this episode we discuss the aspects of unit testing:

Types of changes in code: structural and behavioural
Fast tests make you fast
Learning Tests
Broken console.log
Single asserts in tests
Tests and code handover.
Why trust tests?
Slow tests, leaving process boundaries and unpredictability in tests.
What are: test doubles, mocks, dummies, stubs, spies and fakes?
To mock or not to mock.