Restart identity columns in SQLServer if they exist.

Since SQLServer won't let us truncate tables with foreign keys we can
use delete from and restart the identity sequences.

src/Database/Schema/SqlserverSchema.php

@@ -429,9 +429,21 @@ class SqlserverSchema extends BaseSchema {
  */
 	public function truncateTableSql(Table $table) {
 		$name = $this->_driver->quoteIdentifier($table->name());
-		return [
-			sprintf('TRUNCATE TABLE %s', $name)
+		$queries = [
+			sprintf('DELETE FROM TABLE %s', $name)
 		];
+		$pk = $table->primaryKey();
+		foreach ($pk as $column) {
+			$column = $table->column($column);
+			if (!empty($column['autoIncrement'])) {
+				$queries[] = sprintf(
+					'DBCC CHECKIDENT(%s, RESEED, 0)',
+					$this->_driver->quoteIdentifier($column)
+				);
+				break;
+			}
+		}
+		return $queries;
 	}
 
 }

tests/TestCase/Database/Schema/SqlserverSchemaTest.php

@@ -710,8 +710,9 @@ SQL;
 				'columns' => ['id']
 			]);
 		$result = $table->truncateSql($connection);
-		$this->assertCount(1, $result);
+		$this->assertCount(2, $result);
 		$this->assertEquals('TRUNCATE TABLE [schema_articles]', $result[0]);
+		$this->assertEquals('DBCC CHECKIDENT([schema_articles], RESEED, 0)', $result[1]);
 	}
 
 /**