Contaminated Test Subject
^^^^^
**Definition:**

* A test somehow morphs its subject into something less realistic for its own purposes and without regard for the resulting erosion in our confidence that the test ensures the subject's behavior under real-world conditions.


**Code Example:**

.. code-block:: ruby

  # Subject under test
  require "time"

  class SavingsBond
    def initialize(start_date, mature_value, term_in_years)
      @start_date = start_date
      @mature_value = mature_value
      @term_in_years = term_in_years
    end

    def current_value
      if mature?
        @mature_value
      else
        elapsed = today - @start_date
        term_duration = mature_date - @start_date

        (@mature_value * (elapsed / term_duration)).round
      end
    end
  end

  # Test

  class ContaminatedTestSubject < SmellTest
    def setup
      @subject = SavingsBond.new(
        Time.new(2000, 5, 15),
        1000,
        10
      )
    end

    def test_when_mature_current_value_is_mature_value
      stub(@subject, :mature?, true)

      result = @subject.current_value

      assert_equal 1000, result
    end

    def test_when_immature_current_value_is_prorated
      stub(@subject, :mature?, false)
      stub(@subject, :today, Time.new(2005, 5, 15))

      result = @subject.current_value

      assert_equal 500, result
    end
  end

  # Fake production implementations to simplify example test of subject
  class SavingsBond
    def mature?
      mature_date - Time.new > 0
    end

    def mature_date
      @start_date + term_in_seconds
    end

    def term_in_seconds
      @term_in_years * 365.25 * 24 * 60 * 60
    end

    def today
      Time.new
    end
  end

**References:**

.. admonition:: Quality attributes

    * :octicon:`file-code;1em` -  Code Example
    * :octicon:`comment-discussion;1em` -  Cause and Effect
    * :octicon:`graph;1em` -  Frequency
    * :octicon:`sync;1em` -  Refactoring

* `A workbook repository of example test smells and what to do about them <https://github.com/testdouble/test-smells>`_ :octicon:`file-code;1em` :octicon:`comment-discussion;1em` :octicon:`sync;1em`