False positive uncovered mutant with switch(true) and switch(false)

[luispabon]

Question	Answer
Infection version	0.14.2
Test Framework version	PHPUnit 8.4.3
PHP version	7.2.24/7.3.11/7.4.0-RC4
Platform	Ubuntu/docker
Github Repo	https://github.com/luispabon/favicon-finder
Example	https://infection-php.dev/r/emew

Infection is reporting an uncovered mutant on the repository above:

Not Covered mutants:
====================


1) /home/luis/Projects/favicon/src/Favicon.php:155    [M] TrueValue

--- Original
+++ New
@@ @@
             $links = $dom->getElementsByTagName('link');
             foreach ($links as $link) {
                 /** @var DOMNode $link */
-                switch (true) {
+                switch (false) {
                     case $link->hasAttribute('rel') && strtolower($link->getAttribute('rel')) === 'shortcut icon':
                     case $link->hasAttribute('rel') && strtolower($link->getAttribute('rel')) === 'icon':
                     case $link->hasAttribute('href') && strpos($link->getAttribute('href'), 'favicon') !== false:

This is however a false positive. That line is indeed covered, and the switch from true to false does break tests.

You can check by cloning, composer -o install; make. This runs phpunit and infection in sequence, infection recycling test results from phpunit. Letting infection generate its own reports makes no difference.

Build: https://ci.auronconsulting.co.uk/teams/main/pipelines/favicon-finder-master/jobs/analyze-master/builds/1

[maks-rafalko]

Duplicate of #34

This is how coverage looks like:

It boils down to how PHP works internally, please read exactly the same issue we created earlier #34

See Derick's explanation here https://bugs.xdebug.org/view.php?id=1479#c4450

I would say it won't be fixed on Infection side unless someone wants to do some magic to make it work (similar to how @BackEndTea did it for array coverage)

Closing for now, feel free to reopen, fix, and discuss farther though.

[maks-rafalko]

Probably, as a quick fix, it makes sense to not mutate switch(false) to switch(true) and vice-versa since we know it is always marked as Not Covered. What do you think @luispabon and @infection/core ?

[BackEndTea]

Is the switch never covered? Or only when its switching over true/a constant?

If its never covered we can always skip that; otherwise only for true and false mutator

[maks-rafalko]

Is the switch never covered?

I only saw not covered switch line for true/false. Just tried with an expression, and it is covered

---

Let's do a quick fix to not mutate true -> false, false -> true in a switch. Should fix the issue for now. @luispabon feel free to help with the fix ;)

[luispabon]

Happy to help, could you give me any pointers of where to look? Never got my hands dirty on infection's codebase

[BackEndTea]

Probably somewhere around here:

infection/src/Mutator/Boolean/TrueValue.php

Line 63 in 50c8197

protected function mutatesNode(Node $node): bool

My best bet would be a check to see if the direct parent is the switch statement.

[BackEndTea]

For completeness sake this should also be for the false mutator

[sanmai]

Harder, but better, will be to tag a switch as covered if any single line inside of it is covered.

[BackEndTea]

I think we only need to check the case statements for that. So wed only need to go 1 level deep.

[sanmai]

Or up, unconditionally tagging an uncovered switch as covered every time we see a covered case statement.