PHPLIB-462: Add compatibility traits for the TestCase class

tests/Compat/PolyfillAssertTrait.php

+<?php
+
+namespace MongoDB\Tests\Compat;
+
+use PHPUnit\Framework\Assert;
+use ReflectionClass;
+use Symfony\Bridge\PhpUnit\Legacy\PolyfillAssertTrait as SymfonyPolyfillAssertTrait;
+
+$r = new ReflectionClass(Assert::class);
+if (! $r->hasMethod('assertEqualsWithDelta')) {
+    /**
+     * @internal
+     */
+    trait PolyfillAssertTrait
+    {
+        use SymfonyPolyfillAssertTrait;
+    }
+} else {
+    /**
+     * @internal
+     */
+    trait PolyfillAssertTrait
+    {
+    }
+}

tests/TestCase.php

@@ -7,6 +7,7 @@ use MongoDB\Driver\ReadPreference;
 use MongoDB\Driver\WriteConcern;
 use MongoDB\Model\BSONArray;
 use MongoDB\Model\BSONDocument;
+use MongoDB\Tests\Compat\PolyfillAssertTrait;
 use PHPUnit\Framework\TestCase as BaseTestCase;
 use InvalidArgumentException;
 use ReflectionClass;
@@ -15,6 +16,8 @@ use Traversable;
 
 abstract class TestCase extends BaseTestCase
 {
+    use PolyfillAssertTrait;
+
     /**
      * Return the connection URI.
      *