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Fundamentals of Testing Using Rails

Combine Duplication

Explore how to detect and refactor duplication of fact, logic, and structure in Rails models through test-driven development. Understand practical methods like using constants, instance methods, and encapsulating logic to write cleaner, more maintainable code with custom RSpec matchers.

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We need to look out for three kinds of duplication:

  1. Duplication of fact

  2. Duplication of logic

  3. Duplication of structure

Duplication of fact

Duplication of fact is usually easy to see and fix. A common case is a “magic number” used by multiple parts of the code, such as a conversion factor or a maximum value. We saw this in an earlier example with the 21 days we used to calculate velocity. Another common example is a status variable that has only a few valid values, and the list of those values is duplicated:

Ruby
validates :size, numerically: {less_than_or_equal_to: 5}
def possible_sizes
  (1 .. 5)
end

The remedy for duplication ...