TestConnection: Add return type to setFetchMode

Slipped through in #88 as it's not used at all here.
Now a test exists which does.

src/Test/TestConnection.php

@@ -42,8 +42,9 @@ public function getIterator(): \Iterator
                 return new \ArrayIterator([]);
             }
 
-            public function setFetchMode($mode, ...$args)
+            public function setFetchMode($mode, ...$args): bool
             {
+                return true;
             }
         };
     }

tests/TestConnectionTest.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace ipl\Tests\Sql;
+
+use ipl\Sql\Test\TestConnection;
+
+class TestConnectionTest extends \PHPUnit\Framework\TestCase
+{
+    public function testPrepexec()
+    {
+        $connection = new TestConnection();
+        $stmt = $connection->prepexec('SELECT * FROM foo');
+        $this->assertEmpty(iterator_to_array($stmt));
+        $this->assertTrue($stmt->setFetchMode(\PDO::FETCH_ASSOC));
+    }
+
+    public function testBeginTransaction()
+    {
+        $connection = new TestConnection();
+        $this->expectException(\LogicException::class);
+        $connection->beginTransaction();
+    }
+
+    public function testCommitTransaction()
+    {
+        $connection = new TestConnection();
+        $this->expectException(\LogicException::class);
+        $connection->commitTransaction();
+    }
+
+    public function testRollbackTransaction()
+    {
+        $connection = new TestConnection();
+        $this->expectException(\LogicException::class);
+        $connection->rollbackTransaction();
+    }
+}