Derive mode from DSN function

- Add headers in all files
- Minor field name changes

tests/unit/Mapper/ExistsMapperTest.php

@@ -1,4 +1,10 @@
-<?php declare(strict_types=1);
+<?php
+/**
+ * @author Daniel J. Summers <daniel@bitbadger.solutions>
+ * @license MIT
+ */
+
+declare(strict_types=1);
 
 namespace Test\Unit\Mapper;
 
@@ -17,10 +23,10 @@ class ExistsMapperTest extends TestCase
     public function testMapSucceedsForPostgreSQL(): void
     {
         try {
-            Configuration::$mode = Mode::PgSQL;
+            Configuration::overrideMode(Mode::PgSQL);
             $this->assertFalse((new ExistsMapper())->map([false, 'nope']), 'Result should have been false');
         } finally {
-            Configuration::$mode = null;
+            Configuration::overrideMode(null);
         }
     }
 
@@ -28,17 +34,17 @@ class ExistsMapperTest extends TestCase
     public function testMapSucceedsForSQLite(): void
     {
         try {
-            Configuration::$mode = Mode::SQLite;
+            Configuration::overrideMode(Mode::SQLite);
             $this->assertTrue((new ExistsMapper())->map([1, 'yep']), 'Result should have been true');
         } finally {
-            Configuration::$mode = null;
+            Configuration::overrideMode(null);
         }
     }
 
     public function testMapFailsWhenModeNotSet(): void
     {
         $this->expectException(DocumentException::class);
-        Configuration::$mode = null;
+        Configuration::overrideMode(null);
         (new ExistsMapper())->map(['0']);
     }
 }