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elisp: Test Coverage

 
 17.4 Test Coverage
 ==================
 
 You can do coverage testing for a file of Lisp code by loading the
 ‘testcover’ library and using the command ‘M-x testcover-start <RET>
 FILE <RET>’ to instrument the code.  Then test your code by calling it
 one or more times.  Then use the command ‘M-x testcover-mark-all’ to
 display colored highlights on the code to show where coverage is
 insufficient.  The command ‘M-x testcover-next-mark’ will move point
 forward to the next highlighted spot.
 
    Normally, a red highlight indicates the form was never completely
 evaluated; a brown highlight means it always evaluated to the same value
 (meaning there has been little testing of what is done with the result).
 However, the red highlight is skipped for forms that can’t possibly
 complete their evaluation, such as ‘error’.  The brown highlight is
 skipped for forms that are expected to always evaluate to the same
 value, such as ‘(setq x 14)’.
 
    For difficult cases, you can add do-nothing macros to your code to
 give advice to the test coverage tool.
 
  -- Macro: 1value form
      Evaluate FORM and return its value, but inform coverage testing
      that FORM’s value should always be the same.
 
  -- Macro: noreturn form
      Evaluate FORM, informing coverage testing that FORM should never
      return.  If it ever does return, you get a run-time error.
 
    Edebug also has a coverage testing feature (Coverage
 Testing).  These features partly duplicate each other, and it would be
 cleaner to combine them.
 

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