public function testSettingDefaultPrimary()
 {
     // String
     Blueprint::setDefaultPrimary('category_id');
     $blueprint = new Blueprint('users', function (Blueprint $table) {
         // No primary is specified.
     });
     $result = $blueprint->build();
     $this->assertSame(['category_id'], $result->primary);
     // Array
     Blueprint::setDefaultPrimary(['id', 'category_id']);
     $blueprint = new Blueprint('users', function (Blueprint $table) {
         // No primary is specified.
     });
     $result = $blueprint->build();
     $this->assertSame(['id', 'category_id'], $result->primary);
 }