Add classes and tests from common project

tests/unit/ConfigurationTest.php

@@ -0,0 +1,28 @@
+<?php declare(strict_types=1);
+
+namespace Test\Unit;
+
+use BitBadger\PDODocument\Configuration;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Unit tests for the Configuration class
+ */
+class ConfigurationTest extends TestCase
+{
+    public function testIdFieldDefaultSucceeds(): void
+    {
+        $this->assertEquals('id', Configuration::idField(), 'Default ID field should be "id"');
+    }
+
+    public function testUseIdFieldSucceeds()
+    {
+        try {
+            Configuration::useIdField('EyeDee');
+            $this->assertEquals('EyeDee', Configuration::idField(), 'ID field should have been updated');
+        } finally {
+            Configuration::useIdField('id');
+            $this->assertEquals('id', Configuration::idField(), 'Default ID value should have been restored');
+        }
+    }
+}