Add availability tests for the fall-through functionality

... and run the tests against all PHP versions on which the package can be installed.

This commit:
* Adds a test `bootstrap.php` file which allows for running the tests either via PHPUnit phar files or via a Composer installed version.
* Adds two additional test classes which make sure that the `assertArraySubset()` functionality can be safely used and falls through to the PHPUnit native functionality for PHPUnit < 9.
* Prevents the _real_ unit tests from loading on PHP < 7.3 via an annotation in the `phpunit.xml.dist` file.
    If those files would be loaded on older PHP versions, the test run would break on the parse errors due to modern PHP syntax being used.
* Prevents the _real_ unit tests from running on PHPUnit < 9.
    These tests only need to be run on PHPUnit >= 9 as that is the only time when the polyfills will actually be used.
* Makes a few select exceptions to the coding standards for the new test files for CS rules which require a higher minimum PHP version.
    - `strict_types` is only available as of PHP 7.0.
    - The `void` return type is only available as of PHP 7.1.

Author: jrfnl

phpcs.xml.dist

@@ -29,6 +29,8 @@
         <exclude-pattern>assertarraysubset-autoload\.php</exclude-pattern>
         <exclude-pattern>src/ArraySubsetAssertsEmpty\.php</exclude-pattern>
         <exclude-pattern>src/AssertFallThrough\.php</exclude-pattern>
+        <exclude-pattern>tests/bootstrap\.php</exclude-pattern>
+        <exclude-pattern>tests/Availability/*\.php</exclude-pattern>
     </rule>
     <rule ref="SlevomatCodingStandard.Namespaces.ReferenceUsedNamesOnly.ReferenceViaFullyQualifiedName">
         <exclude-pattern>assertarraysubset-autoload\.php</exclude-pattern>
@@ -40,6 +42,7 @@
     <rule ref="SlevomatCodingStandard.TypeHints.ReturnTypeHint.MissingNativeTypeHint">
         <exclude-pattern>assertarraysubset-autoload\.php</exclude-pattern>
         <exclude-pattern>src/AssertFallThrough\.php</exclude-pattern>
+        <exclude-pattern>tests/Availability/*\.php</exclude-pattern>
     </rule>
 
 </ruleset>

phpunit.xml.dist

@@ -7,11 +7,12 @@
          beStrictAboutOutputDuringTests="true"
          beStrictAboutTodoAnnotatedTests="true"
          beStrictAboutChangesToGlobalState="true"
-         bootstrap="vendor/autoload.php"
+         bootstrap="tests/bootstrap.php"
 >
     <testsuites>
         <testsuite name="unit">
-            <directory>tests</directory>
+            <directory>tests/Availability</directory>
+            <directory phpVersion="7.3.0" phpVersionOperator=">=">tests/Unit</directory>
         </testsuite>
     </testsuites>
 

tests/Availability/AvailibilityViaClassTest.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace DMS\PHPUnitExtensions\ArraySubset\Tests\Availibility;
+
+use DMS\PHPUnitExtensions\ArraySubset\Assert;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Testing that the autoloading of the fall-through `Assert` class for PHPUnit 4.x - 8.x works correctly.
+ *
+ * {@internal The code in this file must be PHP cross-version compatible for PHP 5.4 - current!}
+ */
+final class AvailibilityViaClassTest extends TestCase
+{
+    public function testAssertArraySubsetisAvailabe()
+    {
+        Assert::assertArraySubset([1, 2], [1, 2, 3]);
+    }
+}

tests/Availability/AvailibilityViaTraitTest.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace DMS\PHPUnitExtensions\ArraySubset\Tests\Availibility;
+
+use DMS\PHPUnitExtensions\ArraySubset\ArraySubsetAsserts;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Testing that the autoloading of the empty `ArraySubsetAsserts` trait for PHPUnit 4.x - 8.x works correctly.
+ *
+ * {@internal The code in this file must be PHP cross-version compatible for PHP 5.4 - current!}
+ */
+final class AvailibilityViaTraitTest extends TestCase
+{
+    use ArraySubsetAsserts;
+
+    public function testAssertArraySubsetisAvailabe()
+    {
+        static::assertArraySubset([1, 2], [1, 2, 3]);
+        $this->assertArraySubset([1, 2], [1, 2, 3]);
+    }
+}

tests/Unit/AssertTest.php

@@ -8,6 +8,9 @@
 use PHPUnit\Framework\ExpectationFailedException;
 use PHPUnit\Framework\TestCase;
 
+/**
+ * @requires PHPUnit >= 9
+ */
 final class AssertTest extends TestCase
 {
     public function testAssertArraySubsetPassesStrictConfig(): void

tests/Unit/Constraint/ArraySubsetTest.php

@@ -16,6 +16,9 @@
 
 use function sprintf;
 
+/**
+ * @requires PHPUnit >= 9
+ */
 final class ArraySubsetTest extends TestCase
 {
     /**

tests/bootstrap.php

@@ -0,0 +1,17 @@
+<?php
+/**
+ * PHPUnit bootstrap file.
+ *
+ * {@internal The code in this file must be PHP cross-version compatible for PHP 5.4 - current!}
+ */
+
+if (defined('__PHPUNIT_PHAR__')) {
+    // Testing via a PHPUnit phar.
+    require_once __DIR__ . '/../assertarraysubset-autoload.php';
+} elseif (file_exists(__DIR__ . '/../vendor/autoload.php')) {
+    // Testing via a Composer install.
+    require_once __DIR__ . '/../vendor/autoload.php';
+} else {
+    echo 'Run "composer install" before attempting to run the tests.';
+    exit(1);
+}