functions missing tests: goal of tests?

[mike sander]

It has been asserted in a few threads recently that writing tests is a 
good entry point to octave development.

I have consulted some online resources to determine how to go about 
writing said tests.  Specifically http://wiki.octave.org/Tests has some 
good information.  I was thinking of tackling scripts wiithin 
scripts/general & scripts/miscellaneous as a starting point.

Software testing is a rather broad field.  "write tests for untested 
functions" is a rather vague notion.  I am trying to get my head around 
"what are the requirements?", "what needs to be tested"? etc.  I am 
putting out a call for some guidance in this regard.

As i understand it, the tests within m files (and probably cc) are unit 
tests... and probably within the "grey box" testing category.    ie. 
testing the code for various inputs to produce desired outputs, while 
having some knowledge of the inner workings of said code.

Given the above I believe the purpose of the tests with m files is to 
test correct behavior of these functions across a representative set of 
data types / data values.  This includes returning an error for invalid 
inputs.   Is this consistent with how other maintainers view m file 
tests?   Should the tests include other criterion?   An example could be 
100% code coverage.  Personally, I would include 100 % code coverage as 
a future goal.

Are there other requirements at a function level that I may be 
missing?   Ideally tests should capture those as well.   A link to said 
documentation would be appreciated.