When you ask Testcover to cover code containing a vector which
contains a dotted pair, it results in an error.  I introduced this
bug when I rewrote Testcover last year.

To reproduce first save this snippet in a file called bug.el:

(defun my-func ()
  (equal (vector '(8 . "xxx")) [(8 . "xxx")]))

Then:

M-x testcover-start RET bug.el RET

Result: Wrong type argument: listp, "xxx"

Here's a patch to fix this.  While I was adding a test for it, I
noticed that the docstrings for all of Testcover's tests still mention
reinstrumenting, but Testcover now analyzes code instead of
reinstrumenting it, so I also updated the docstrings.