Unit testing Angular applications is important to ensure components and services work as expected. There are several frameworks that can be used for Angular unit testing, including Jasmine for writing tests and Karma as a test runner. Key aspects of unit testing covered in the document include: using test doubles like stubs and spies to isolate the system under test; focusing tests on small units and targeting specific assertions; and dealing with asynchronous code. The document also provides examples of writing pure unit tests in Jasmine without dependencies and using spies to control dependencies.