Add a bit more documentation and fix up tests.

src/Database/Expression/IdentifierExpression.php

@@ -18,7 +18,12 @@ use Cake\Database\ExpressionInterface;
 use Cake\Database\ValueBinder;
 
 /**
- * Represents a single identifier name in the database
+ * Represents a single identifier name in the database.
+ *
+ * Identifier values are unsafe with user supplied data.
+ * Values will be quoted when identifier quoting is enabled.
+ *
+ * @see \Cake\Database\Query::identifier()
  */
 class IdentifierExpression implements ExpressionInterface
 {

tests/TestCase/Database/QueryTest.php

@@ -16,7 +16,6 @@ namespace Cake\Test\TestCase\Database;
 
 use Cake\Database\Expression\IdentifierExpression;
 use Cake\Database\ExpressionInterface;
-use Cake\Database\IdentifierInterface;
 use Cake\Database\Query;
 use Cake\Database\StatementInterface;
 use Cake\Database\TypeMap;
@@ -3394,13 +3393,9 @@ class QueryTest extends TestCase
     public function testIdentifierInterface()
     {
         $query = new Query($this->connection);
-        /* @var \Cake\Database\IdentifierInterface $identifier */
         $identifier = $query->identifier('description');
 
-        // should support these interfaces
-        $this->assertInstanceOf(IdentifierInterface::class, $identifier);
         $this->assertInstanceOf(ExpressionInterface::class, $identifier);
-
         $this->assertEquals('description', $identifier->getIdentifier());
 
         $identifier->setIdentifier('title');