Test Driven Development

What are the aims / what is the point of TDD? One of the primary aims of unit testing is to isolate a method or component that you want to test and see how it behaves under a variety of circumstances. 

How to write testable Javascript: Externalize all javascript - don't write inline as it can't be tested. Provide a public interface - it's difficult to test private methods Use instantiable objects Flatten the pyramid of doom: avoid many nested levels of callbacks Separate DOM event handlers from the actions they perform: e.g. separate submit button click from form submit. Mock in XHR requests

The process of test driven development: You first write a test for a function before you write the function itself You create a failing test initially, rounding this out with passing tests. You then build the actual functionality of the function. Run the tests to see that you get the expected results. After that you wrinse and repeat.

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