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Testing through the Credit Crunch - Part 2 - Test Driven Development

Sun 30 Nov 2008

In the last post of this series I discussed briefly about Technical Debt and how Test Driven Development can help in dropping the debt and dropping the amount of interest gained over the life of the product.

Test Driven Development is the concept that you write your tests before you write your code. Once your code is finished you refactor with the safety that your newly created test will prevent any stupid bugs that you could have introduced. It's what the TDD community call Red-Green-Refactor. Now to most people writing tests first sounds stupid, "How do you know what your code is going to do until you have finished coding it?" My retort tends to be "You know what you are expecting back from the call. Your test needs to be really small and since an Assert is a test, Assert what you are expecting your method to return! Image that your code exists and test against it." Below is an example of a small test and when writing tests we should try keep them as small as we physically can.

public void creditcrunch_Test(){
  int FutureTechnicalDebt = 100;

So we know that we need tests first to give us a good safety net for writing our code.In Technical Debt terms we have spent a little less to create/run and report on the test and we prevent anyone else breaking our code. Cost-- and Interest-- which is what we want. Running the test above will fail because there is no code to run it against. Write some code to make it pass if you have the time.

The other reason why developers are starting to like TDD, other than the removal of the ear ache that testers would give them about throwaway builds, is that challenges them to think about the interface into their new object. We have all sat down with the keyboard in front of us, tea/coffee next to us and found that someone has changed the interface your were developing against! Queue the expletives! Luckily for us we have good Test Driven Developers who have have discussed the interface and we by proxy prevented interest being added to our debt. Interest--! Communication is key in Test Driven Developments, especially when it comes to interfaces because there may be some integration bugs that will creep in without you realising!

Knowing what the Interface is going to look like is has another major benefit. Mocks and stubs! If we know what the interface to an assembly is and how its going to react we can write tests to test our code and when it needs to speak to the other assembly, which may not have been created yet or makes our tests run slowly like accessing a database or filesystem, we can return the results back that we want our code to handle using one of them. This could be exceptions,dodgy data or good data. Testing those code paths means we can increase our code coverage therefore increasing the size of our safety net! It will also mean that our tests run a lot quicker because we don't have to interact with slow drives or have anyone elses tests interfere with our data. Cost-- and Interest--.

So by creating this safety net we have prevented stupid mistakes creeping into our code. Its these stupid mistakes that could cost our team/company a lot of money. Since companies don't have much money it could mean your job!

The graph below shows how by doing the, what I call, simple things we have brought down the technical debt that we could potentially owe. NOTE: The values used are just arbitary values I found on the internet with a little searching.

project cost

In the next post in the series I will discuss Virtualization and what the it can mean to you as a tester!

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