Tests: allow the test suite to run on PHPUnit 8.x and 9.x

Includes:
* `composer.json`: widening the PHPUnit requirement to allow for PHPUnit 8.x and PHPUnit 9.x.
    Note: The recently released PHPUnit 10.x is not (yet) supported as it no longer supports the old-style test suite runner setup.
    It also would require for the abstract base test cases to be renamed as those classes are no longer allowed to end on `Test`.
    Refactoring the test suite to allow for PHPUnit 10.x is for a future PR.
* Adjusting the PHPUnit configuration to ensure the tests are run in the same way and show all notices/warnings/deprecations on all PHPUnit versions.
    The default value for a number of configuration options has changed over time.
    This makes sure they are consistently set to values which are sensible for this codebase, independently of the PHPUnit version on which the tests are run.
    Includes adding a schema annotation (set to PHPUnit 9.2 as the schema has changed in PHPUnit 9.3, though that won't prevent the tests from running correctly).
* GH Actions `test` workflow: removing work-arounds which were in place related to running PHPUnit 7.x on PHP 8.x.
* `AllTests`: Adjusting the condition which determines which `TestSuite` file to load to allow for PHPUnit 8.x and 9.x.
* Adding the `.phpunit.result.cache` file to `.gitignore`.
    PHPUnit has a caching feature build in as of PHPUnit 8, so ignore the file that generates to prevent it from being committed.

Related to 3395

Author: jrfnl

.github/workflows/test.yml

@@ -114,37 +114,20 @@ jobs:
 
       # Install dependencies and handle caching in one go.
       # @link https://github.com/marketplace/actions/install-composer-dependencies
-      - name: Install Composer dependencies - normal
-        if: ${{ matrix.php < '8.0' }}
+      - name: Install Composer dependencies
         uses: "ramsey/composer-install@v2"
         with:
           # Bust the cache at least once a month - output format: YYYY-MM.
           custom-cache-suffix: $(date -u "+%Y-%m")
 
-      # For PHP 8.0+, we need to install with ignore platform reqs as PHPUnit 7 is still used.
-      - name: Install Composer dependencies - with ignore platform
-        if: ${{ matrix.php >= '8.0' }}
-        uses: "ramsey/composer-install@v2"
-        with:
-          composer-options: --ignore-platform-reqs
-          custom-cache-suffix: $(date -u "+%Y-%m")
-
       # Note: The code style check is run multiple times against every PHP version
       # as it also acts as an integration test.
       - name: 'PHPCS: set the path to PHP'
         run: php bin/phpcs --config-set php_path php
 
       - name: 'PHPUnit: run the tests'
-        if: ${{ matrix.php != '8.1' && matrix.php != '8.2' }}
         run: vendor/bin/phpunit tests/AllTests.php
 
-      # We need to ignore the config file so that PHPUnit doesn't try to read it.
-      # The config file causes an error on PHP 8.1+ with PHPunit 7, but it's not needed here anyway
-      # as we can pass all required settings in the phpunit command.
-      - name: 'PHPUnit: run the tests on PHP > 8.0'
-        if: ${{ matrix.php == '8.1' || matrix.php == '8.2' }}
-        run: vendor/bin/phpunit tests/AllTests.php --no-configuration --bootstrap=tests/bootstrap.php --dont-report-useless-tests
-
       - name: 'PHPCS: check code style without cache, no parallel'
         if: ${{ matrix.custom_ini == false && matrix.php != '7.4' }}
         run: php bin/phpcs --no-cache --parallel=1

.gitignore

@@ -4,3 +4,4 @@
 .idea/*
 /vendor/
 composer.lock
+.phpunit.result.cache

composer.json

@@ -32,7 +32,7 @@
         "ext-simplexml": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.0 || ^5.0 || ^6.0 || ^7.0"
+        "phpunit/phpunit": "^4.0 || ^5.0 || ^6.0 || ^7.0 || ^8.0 || ^9.0"
     },
     "bin": [
         "bin/phpcs",

phpunit.xml.dist

@@ -1,5 +1,15 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit beStrictAboutTestsThatDoNotTestAnything="false" bootstrap="tests/bootstrap.php">
+<phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.2/phpunit.xsd"
+    backupGlobals="true"
+    beStrictAboutTestsThatDoNotTestAnything="false"
+    bootstrap="tests/bootstrap.php"
+    convertErrorsToExceptions="true"
+    convertWarningsToExceptions="true"
+    convertNoticesToExceptions="true"
+    convertDeprecationsToExceptions="true"
+    >
     <testsuites>
         <testsuite name="PHP_CodeSniffer Test Suite">
             <file>tests/AllTests.php</file>

tests/AllTests.php

@@ -24,7 +24,7 @@
 $phpunit7 = false;
 if (class_exists('\PHPUnit\Runner\Version') === true) {
     $version = \PHPUnit\Runner\Version::id();
-    if ($version[0] === '7') {
+    if (version_compare($version, '7.0', '>=') === true) {
         $phpunit7 = true;
     }
 }