Add PostgreSQL Support (#3)

Reviewed-on: #3

tests/integration/sqlite/ExistsTest.php

@@ -2,7 +2,7 @@
 
 namespace Test\Integration\SQLite;
 
-use BitBadger\PDODocument\{Exists, Field};
+use BitBadger\PDODocument\{DocumentException, Exists, Field};
 use PHPUnit\Framework\Attributes\TestDox;
 use PHPUnit\Framework\TestCase;
 
@@ -51,4 +51,18 @@ class ExistsTest extends TestCase
         $this->assertFalse(Exists::byFields(ThrowawayDb::TABLE, [Field::LT('nothing', 'none')]),
             'There should not have been any existing documents');
     }
+
+    public function testByContainsFails(): void
+    {
+        $this->expectException(DocumentException::class);
+        Exists::byContains('', []);
+    }
+
+    #[TestDox('By JSON Path fails')]
+    public function testByJsonPathFails(): void
+    {
+        $this->expectException(DocumentException::class);
+        Exists::byJsonPath('', '');
+    }
 }
+