Add some unit tests for Providers\ServerVariables classes

Signed-off-by: Maurício Meneghini Fauth <mauricio@mfauth.net>

tests/unit/Providers/ServerVariables/ServerVariablesProviderTest.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpMyAdmin\Tests\Providers\ServerVariables;
+
+use PhpMyAdmin\Providers\ServerVariables\ServerVariablesProvider;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use ReflectionProperty;
+
+#[CoversClass(ServerVariablesProvider::class)]
+final class ServerVariablesProviderTest extends TestCase
+{
+    public function testUniqueness(): void
+    {
+        (new ReflectionProperty(ServerVariablesProvider::class, 'instance'))->setValue(null, null);
+        $instanceOne = ServerVariablesProvider::getImplementation();
+        $instanceTwo = ServerVariablesProvider::getImplementation();
+        self::assertSame($instanceOne, $instanceTwo);
+    }
+}

tests/unit/Providers/ServerVariables/VoidProviderTest.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpMyAdmin\Tests\Providers\ServerVariables;
+
+use PhpMyAdmin\Providers\ServerVariables\VoidProvider;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+
+#[CoversClass(VoidProvider::class)]
+final class VoidProviderTest extends TestCase
+{
+    public function testVoidProvider(): void
+    {
+        $provider = new VoidProvider();
+        self::assertNull($provider->getVariableType('test'));
+        self::assertSame([], $provider->getStaticVariables());
+        self::assertNull($provider->getDocLinkByNameMariaDb('test'));
+        self::assertNull($provider->getDocLinkByNameMysql('test'));
+    }
+}