Skip to main content

Write Assertions First

Writing a test as part of the TDD process is simple.

  1. Arrange
  2. Act
  3. Assert

Many individuals recommend the process be reversed. Write assertions first. Then write the steps to perform the action. Followed by the required setup to complete the action.

  1. Arrange
  2. Act
  3. Assert

Simplicity

You will write just enough of the test to do the job. Its not far from doing TDD on the test itself. Using staticily compiled languages you would see compile time errors while performing this step. As you are writing the test in reverse this is normal and expected. Most text editors or IDE's can ease this process.

Implement just enough of the test to do your job. The opposite of this is large, copy/paste tests that require lines of setup code that can safely be removed or reduced.

Meaning

You end up naming variables with more meaning. With a traditional approach variables can lack true, descriptive names. They are often called result or similar. By working in reverse you force yourself to think of what you are asserting upon. This forces better names out in the process. An example would be orderTotals if the purpose of the assertion was to check if the total of an order was as expected.

Writing assertions first can feel awkward but the benefits of this change are well worth the initial slowdown.

Comments

  1. Great technique, thanks for sharing!

    Without some extra effort I have found I frequently end with tests that verify a bit too much. Applying this had immediate positive impact :)

    ReplyDelete

Post a Comment

Popular posts from this blog

Constant Object Anti Pattern

Most constants are used to remove magic numbers or variables that lack context. A classic example would be code littered with the number 7. What does this refer to exactly? If this was replaced with DaysInWeek or similar, much clarity is provided. You can determine that code performing offsets would be adding days, rather than a mysterious number seven.Sadly a common pattern which uses constants is the use of a single constant file or object. The beauty of constants is clarity, and the obvious fact such variables are fixed. When a constant container is used, constants are simply lumped together. These can grow in size and often become a dumping ground for all values within the application.A disadvantage of this pattern is the actual value is hidden. While a friendly variable name is great, there will come a time where you will want to know the actual value. This forces you to navigate, if only to peek at the value within the constant object. A solution is to simple perform a refactor …

Three Steps to Code Quality via TDD

Common complaints and problems that I've both encountered and hear other developers raise when it comes to the practice of Test Driven Development are: Impossible to refactor without all the tests breakingMinor changes require hours of changes to test codeTest setup is huge, slow to write and difficult to understandThe use of test doubles (mocks, stubs and fakes is confusing)Over the next three posts I will demonstrate three easy steps that can resolve the problems above. In turn this will allow developers to gain one of the benefits that TDD promises - the ability to refactor your code mercifully in order to improve code quality.StepsStop Making Everything PublicLimit the Amount of Dependencies you Use A Unit is Not Always a Method or ClassCode quality is a tricky subject and highly subjective, however if you follow the three guidelines above you should have the ability to radically change implementation details and therefore improve code quality when needed.

DRY vs DAMP in Tests

In the previous post I mentioned that duplication in tests is not always bad. Sometimes duplication becomes a problem. Tests can become large or virtually identically excluding a few lines. Changes to these tests can take a while and increase the maintenance overhead. At this point, DRY violations need to be resolved.SolutionsTest HelpersA common solution is to extract common functionality into setup methods or other helper utilities. While this will remove and reduce duplication this can make tests a bit harder to read as the test is now split amongst unrelated components. There is a limit to how useful such extractions can help as each test may need to do something slightly differently.DAMP - Descriptive and Meaningful PhrasesDescriptive and Meaningful Phrases is the alter ego of DRY. DAMP tests often use the builder pattern to construct the System Under Test. This allows calls to be chained in a fluent API style, similar to the Page Object Pattern. Internally the implementation wil…