Hi team, this issue was inspired by, and is somewhat related to MDL-76506.

If a process executes two files that have say,

file1:

include "$CFG->dirroot/lib/setup.php";

file2:

require("$CFG->dirroot/lib/setup.php"); 

This will cause `MDL_PERF`, `MDL_PERFDB`, and `MDL_PERFTOFOOT` to be defined as `true`, even if they are not defined in the configuration.

An example of this could be the following:

Steps to replicate

1. Make sure there is a line to the same effect of (or copy this one) `require("$CFG->dirroot/lib/setup.php");` in your 'config.php' file (or equivalent configuration file that you use). Put a breakpoint on this line.
2. On https://github.com/moodle/moodle/blob/master/lib/phpunit/bootstrap.php#L217 you can see that it contains `require("$CFG->dirroot/lib/setup.php");` which is the second require of 'lib/setup.php'. Put a breakpoint on this line as well.
3. Setup the PhpUnit environment, and listen for debugging connections with Xdebug or similar.
4. Run any PhpUnit test, e.g. `php vendor/bin/phpunit admin/tool/mobile/tests/api_test.php --filter test_get_autologin_key`.
5. When you trip the breakpoint from step 1, step into that line, and execute the 'lib/setup.php' file until the line that says `if (!defined('MDL_PERF_TEST')) {`. Step over. In this first pass, `MDL_PERF_TEST` is defined as false.
6. Continue execution, when the second breakpoint is tripped from step 2, step into that line, and like in step 5, continue execution up to the line that says `if (!defined('MDL_PERF_TEST')) {`. Step over a few times. In this second pass `MDL_PERF`, `MDL_PERFDB`, and `MDL_PERFTOFOOT` are defined as `true`.

Observed behavior

The constants `MDL_PERF`, `MDL_PERFDB`, and `MDL_PERFTOFOOT` are defined as `true` even when they are not defined in the configuration of the site.

Expected behavior

The constants `MDL_PERF`, `MDL_PERFDB`, and `MDL_PERFTOFOOT` are not defined, unless defined in the configuration.

Possible solution

This seems like one of those cases where the `if` can be extended from:

if (!defined('MDL_PERF_TEST')) { 

to:

if (!defined('MDL_PERF_TEST') || !MDL_PERF_TEST) { 

such that when `MDL_PERF_TEST` is already defined but is `false`, the same flow of execution is followed... I tested this solution and it works, but it produces a PHP Notice (because `MDL_PERF_TEST` was already defined in the first pass), so this may not be the appropriate solution. I guess that another solution would be to enclose the `ifs` of `MDL_PERF`, `MDL_PERFDB`, and `MDL_PERFTOFOOT`, into an `if (MDL_PERF_TEST) {`. I tested that too and it worked, without producing a PHP Notice.

Thank you for your attention to the present issue.