Very simple integration tests to verify that command line works ok

As far as unit tests don't use the command line tools (phpcs, phpcbf)
they can be passing ok while the tools have some other problem
(say php X.Y compatibility or whatever).

These tests just ensure that the command line tools are executed
once, against a simple fixture file and results are the expected
ones (we have used very simple shell exit codes checks,
that's enough for now).

Also note that, iby default, the php action comes with production
php.ini settings, so error levels and output are not the best
for CIs. Hence, let's enable them here.

Reference: shivammathur/setup-php#450

.github/workflows/phpcs.yml

@@ -22,7 +22,7 @@ jobs:
         with:
           php-version: ${{ matrix.php }}
           extensions: ${{ matrix.extensions }}
-          ini-values: pcov.directory=moodle
+          ini-values: pcov.directory=moodle, error_reporting=-1, display_errors=On
           coverage: pcov
           tools: composer
 
@@ -46,3 +46,13 @@ jobs:
 
       - name: Test coverage
         run: ./vendor/bin/phpunit-coverage-check -t 80 clover.xml
+
+      - name: Integration tests
+        if: ${{ always() }}
+        run: |
+          # There is one failure (exit with error)
+          vendor/bin/phpcs --standard=moodle moodle/Tests/fixtures/integration_test_ci.php ||
+          # The failure is fixed (exit with error)
+          vendor/bin/phpcbf --standard=moodle moodle/Tests/fixtures/integration_test_ci.php ||
+          # So, there isn't any failure any more (exit without error)
+          vendor/bin/phpcs --standard=moodle moodle/Tests/fixtures/integration_test_ci.php

moodle/Tests/fixtures/integration_test_ci.php

@@ -0,0 +1,4 @@
+<?php
+// phpcs:disable moodle.Files
+defined('MOODLE_INTERNAL') || die(); // Make this always the 1st line in all CS fixtures.
+$arr ['wrong'] = $value;