How to detect an undefined method?

[anthony.flury]

On 27/03/2022 15:59, dn wrote:

> What is code coverage?
> In the simplest words, code coverage is a measure of exhaustiveness of a
> test suite. 100% code coverage means that a system is fully tested.

Sorry, but that is a gross over-simplification.

100% coverage means that you have tested all of the branches in a given 
module, or a given class; it absolutely does not mean it is fully tested.

For example I can write code and unit-test cases for a trivial piece of 
code, and to achieve 100% coverage, but for the code to still fail on 
invalid input data, or for the code to fail due to exceptions from 
library code that my code doesn't handle.

To claim to be fully tested a piece of code has to be exercised against 
*every* possible input and *every* single possible event from *every* 
single source - that alone makes 100% testing impossible. If you think 
logically about it, you can only test a very small fraction of all 
possible test cases; the key is to pick those cases which represent a 
good range of possible inputs and events (including both valid and 
invalid data, exceptions, errors etc).

At best 100% coverage measure means that every branch through the code 
has been executed at least once by your test cases. It doesn't prove 
that your test cases are complete, or that your code takes into account 
all possible occurrences - 100% coverage doesn't mean it is fully tested.

In terms of coverage,  achieving 100% coverage is a laudable target, but 
it is often either unachievable or not worth the effort; aiming to 
achieve a high value (say > 80%) is sensible target.

If you achieve your high coverage count by doing black-box testing (ie. 
by testing to the specification of code and thinking what can right and 
what can go wrong), then the coverage is a more useful measure - if you 
write your unit-tests by looking at the code, then all that a high 
measurement means is that you are able (mostly) to read and understand 
your own code.

-- 
Anthony Flury
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