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Subject: |
26.0.50; Testcover doesn't work on code that creates simple lists and modifies them |
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Date: |
Tue, 03 Jan 2017 19:06:17 -0800 |
Testcover marks forms which have only returned a single value while under
code coverage with a tan splotch to indicate insufficient test coverage,
It also identifies forms which will only ever return a single value and
suppresses the splotch on those. During the coverage run, it saves a
reference to the return value of those single value forms, and the next
time the form is evaluated, it uses `equal' to determine if the value
has changed, and if it has, Testcover reports an error.
The problem with this is that it is a common idiom to create a data
structure using an expression that always returns the same thing, and
then modify it later. Since Testcover keeps a reference not a copy, it
ends up with a reference to a modified object, which fails the
comparison with the next return value of the same expression.
For example:
(defun my-blank-record ()
(list (list 'name) (list 'age)))
(defun my-make-record (name age)
(let ((rec (my-blank-record)))
(setf (cdr (assq 'name rec)) name)
(setf (cdr (assq 'age rec)) age)
rec))
(my-make-record "Jack" 10)
(my-make-record "Jill" 12)
To reproduce this problem, save the above code in a file called bug.el,
and then:
M-x testcover-start RET bug.el RET
The result will be testcover-1value's "Value of form marked with
‘1value’ does vary" error.
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