[core] add a test suite for SQL features

core/dbengine.php

@@ -44,6 +44,7 @@ class MySQL extends DBEngine
     public function init(PDO $db): void
     {
         $db->exec("SET NAMES utf8;");
+        $db->exec("SET SESSION sql_mode='ANSI,TRADITIONAL';");
     }
 
     public function scoreql_to_sql(string $data): string

core/tests/SQLTest.php

@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shimmie2;
+
+/**
+ * Because various SQL engines have wildly different support for
+ * various SQL features, and sometimes they are silently incompatible,
+ * here's a test suite to ensure that certain features give predictable
+ * results on all engines and thus can be considered safe to use.
+ */
+class SQLTest extends ShimmiePHPUnitTestCase
+{
+    public function testConcatPipes(): void
+    {
+        global $database;
+        $this->assertEquals(
+            "foobar",
+            $database->get_one("SELECT 'foo' || 'bar'")
+        );
+    }
+}