File: testcover.el.html

* Use testcover-start to instrument a Lisp file for coverage testing.

* Use testcover-mark-all to add overlay "splotches" to the Lisp file's
  buffer to show where coverage is lacking. Normally, a red splotch
  indicates the form was never evaluated; a brown splotch means it always
  evaluated to the same value.
* Use testcover-next-mark (bind it to a key!) to jump to the next spot
  that has a splotch.

* Basic algorithm: use edebug to mark up the function text with
  instrumentation callbacks, walk the instrumented code looking for
  forms which don't return or always return the same value, then use
  Edebug's before and after hooks to replace its code coverage with ours.
* To show good coverage, we want to see two values for every form, except
  functions that always return the same value and defconst variables
  need show only one value for good coverage. To avoid the brown
  splotch, the definitions for constants and 1-valued functions must
  precede the references.
* Use the macro 1value in your Lisp code to mark spots where the local
  code environment causes a function or variable to always have the same
  value, but the function or variable is not intrinsically 1-valued.
* Use the macro noreturn in your Lisp code to mark function calls that
  never return, because of the local code environment, even though the
  function being called is capable of returning in other cases.

Problems:
* equal, which is used to compare the results of repeatedly executing
  a form, has a couple of shortcomings. It considers strings to be the same
  if they only differ in properties, and it raises an error when asked to
  compare circular lists.
* Because we have only a "1value" class and no "always nil" class, we have
  to treat as potentially 1-valued any and whose last term is 1-valued,
  in case the last term is always nil. Example: (and (< (point) 1000) (forward-char 10)) This form always returns nil. Similarly, or, if, and cond are treated as potentially 1-valued if all clauses are, in case those values are always nil. Unlike truly 1-valued functions, it is not an error if these "potentially" 1-valued forms actually return differing values.

Defined variables (11)

Defined functions (23)

Defined faces (2)