Register all of /tests/src/ for class loading

+1 just ran into this myself

+1 this would simplify phpstan-drupal's autoloader for Drupal: https://github.com/mglaman/phpstan-drupal/blob/main/src/Drupal/DrupalAut...

    protected function addCoreTestNamespaces(): void
    {
        // Add core test namespaces.
        $core_tests_dir = $this->drupalRoot . '/core/tests/Drupal';
        $this->namespaces['Drupal\\BuildTests'] = $core_tests_dir . '/BuildTests';
        $this->namespaces['Drupal\\FunctionalJavascriptTests'] = $core_tests_dir . '/FunctionalJavascriptTests';
        $this->namespaces['Drupal\\FunctionalTests'] =  $core_tests_dir . '/FunctionalTests';
        $this->namespaces['Drupal\\KernelTests'] = $core_tests_dir . '/KernelTests';
        $this->namespaces['Drupal\\Tests'] = $core_tests_dir . '/Tests';
        $this->namespaces['Drupal\\TestSite'] = $core_tests_dir . '/TestSite';
        $this->namespaces['Drupal\\TestTools'] = $core_tests_dir . '/TestTools';
        $this->namespaces['Drupal\\Tests\\TestSuites'] = $this->drupalRoot . '/core/tests/TestSuites';
    }

I vaguely recall that the reason we did that was because it was unclear how the tests would be organized as we got closer to 8.0.0 release, and we wanted to avoid simpletest-based tests.

It's still the case that a contrib module might use the (now-contrib) simpletest module for some testing, so the guardrails might still be needed, unless, of course, an actual subsystem maintainer says otherwise.

According to TestDiscovery there should be no conflict with simpletest namespaces or paths:

      // Add Simpletest test namespace.
      $this->testNamespaces["Drupal\\$name\\Tests\\"][] = "$base_path/src/Tests";

      // Add PHPUnit test namespaces.
      $this->testNamespaces["Drupal\\Tests\\$name\\Unit\\"][] = "$base_path/tests/src/Unit";
      $this->testNamespaces["Drupal\\Tests\\$name\\Kernel\\"][] = "$base_path/tests/src/Kernel";
      $this->testNamespaces["Drupal\\Tests\\$name\\Functional\\"][] = "$base_path/tests/src/Functional";
      $this->testNamespaces["Drupal\\Tests\\$name\\Build\\"][] = "$base_path/tests/src/Build";
      $this->testNamespaces["Drupal\\Tests\\$name\\FunctionalJavascript\\"][] = "$base_path/tests/src/FunctionalJavascript";

ie. Simpletest tests live in $module/src/Tests but PHPUnit tests live in $module/tests/src

We should also remove the remaining Simpletest support from core anyway, please see #3254726: Remove SimpleTest support from run-tests.sh, TestDiscovery and TestRunnerKernel for that.

Let's see what happens if we do module tests first.

If this passes we can try the core test locations identified in #3 as well.

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Attached patch against Drupal 10.1.x

Patch #7 is not applied for Drupal 10.1.x so Inter-diff file is not added.

Checking patch core/lib/Drupal/Core/Test/TestDiscovery.php...
error: while searching for:
$this->testNamespaces["Drupal\\$name\\Tests\\"][] = "$base_path/src/Tests";

// Add PHPUnit test namespaces.
$this->testNamespaces["Drupal\\Tests\\$name\\Unit\\"][] = "$base_path/tests/src/Unit";
$this->testNamespaces["Drupal\\Tests\\$name\\Kernel\\"][] = "$base_path/tests/src/Kernel";
$this->testNamespaces["Drupal\\Tests\\$name\\Functional\\"][] = "$base_path/tests/src/Functional";
$this->testNamespaces["Drupal\\Tests\\$name\\Build\\"][] = "$base_path/tests/src/Build";
$this->testNamespaces["Drupal\\Tests\\$name\\FunctionalJavascript\\"][] = "$base_path/tests/src/FunctionalJavascript";

// Add discovery for traits which are shared between different test
// suites.
$this->testNamespaces["Drupal\\Tests\\$name\\Traits\\"][] = "$base_path/tests/src/Traits";
}

foreach ($this->testNamespaces as $prefix => $paths) {

error: patch failed: core/lib/Drupal/Core/Test/TestDiscovery.php:102
error: core/lib/Drupal/Core/Test/TestDiscovery.php: patch does not apply
Checking patch core/tests/bootstrap.php...
Hunk #1 succeeded at 79 (offset -1 lines).
Hunk #2 succeeded at 87 (offset -1 lines).

Needs work per #7/ #3

I've tested the patch in #11 on Drupal 10.2 and confirmed that this fixes the issue with test classes being unable to find a helper class under tests/src/Helper within a module test directory, as described in the steps to reproduce. Similarly I've verified this for theme and profile test directories.

What additional work is needed for core test locations (#7), and could this be split to another issue so the existing fix for modules, themes and profiles can be RTBC?

I don't actually think we can do much about the core namespaces, because they sit directly under \Drupal and we don't want to go looking in core/tests/Drupal for non-test Drupal code.

Converted #11 to an MR, inlined a variable for readability, and updated the IS with the proposed solution.

Hiding patches.

Seems to have a test failure.

Just needed rebase.

Sweet. Change didn’t break anything

Committed/pushed to 11.x and cherry-picked to 10.3.x, thanks!