Add Tests Cases to Demonstrate #2906

Postgres has a `SERIAL` data type to allow shorthand for
`nextval('sequence_name')`, but DDL like this:

    CREATE TABLE example (id SERIAL)

Cannot be generated in the DBAL schema APIs.

tests/Doctrine/Tests/DBAL/Functional/Schema/PostgreSqlSchemaManagerTest.php

@@ -419,6 +419,50 @@ class PostgreSqlSchemaManagerTest extends SchemaManagerFunctionalTestCase
         $this->assertEquals(-1.1, $columns['col_decimal']->getDefault());
         $this->assertEquals('(-1)', $columns['col_string']->getDefault());
     }
+
+    public static function serialTypes() : array
+    {
+        return [
+            ['integer'],
+            ['bigint'],
+        ];
+    }
+
+    /**
+     * @dataProvider serialTypes
+     * @group 2906
+     */
+    public function testAutoIncrementCreatesSerialDataTypesWithoutADefaultValue(string $type) : void
+    {
+        $tableName = "test_serial_type_$type";
+
+        $table = new Schema\Table($tableName);
+        $table->addColumn('id', $type, ['autoincrement' => true, 'notnull' => false]);
+
+        $this->_sm->dropAndCreateTable($table);
+
+        $columns = $this->_sm->listTableColumns($tableName);
+
+        self::assertNull($columns['id']->getDefault());
+    }
+
+    /**
+     * @dataProvider serialTypes
+     * @group 2906
+     */
+    public function testAutoIncrementCreatesSerialDataTypesWithoutADefaultValueEvenWhenDefaultIsSet(string $type) : void
+    {
+        $tableName = "test_serial_type_with_default_$type";
+
+        $table = new Schema\Table($tableName);
+        $table->addColumn('id', $type, ['autoincrement' => true, 'notnull' => false, 'default' => 1]);
+
+        $this->_sm->dropAndCreateTable($table);
+
+        $columns = $this->_sm->listTableColumns($tableName);
+
+        self::assertNull($columns['id']->getDefault());
+    }
 }
 
 class MoneyType extends Type

tests/Doctrine/Tests/DBAL/Platforms/AbstractPostgreSqlPlatformTestCase.php

@@ -144,6 +144,63 @@ abstract class AbstractPostgreSqlPlatformTestCase extends AbstractPlatformTestCa
         $this->assertEquals(array('CREATE TABLE autoinc_table (id SERIAL NOT NULL)'), $this->_platform->getCreateTableSQL($table));
     }
 
+    public static function serialTypes() : array
+    {
+        return [
+            ['integer', 'SERIAL'],
+            ['bigint', 'BIGSERIAL'],
+        ];
+    }
+
+    /**
+     * @dataProvider serialTypes
+     * @group 2906
+     */
+    public function testGenerateTableWithAutoincrementDoesNotSetDefault(string $type, string $definition) : void
+    {
+        $table  = new \Doctrine\DBAL\Schema\Table('autoinc_table_notnull');
+        $column = $table->addColumn('id', $type);
+        $column->setAutoIncrement(true);
+        $column->setNotNull(false);
+
+        $sql = $this->_platform->getCreateTableSQL($table);
+
+        self::assertEquals(["CREATE TABLE autoinc_table_notnull (id $definition)"], $sql);
+    }
+
+    /**
+     * @dataProvider serialTypes
+     * @group 2906
+     */
+    public function testCreateTableWithAutoincrementAndNotNullAddsConstraint(string $type, string $definition) : void
+    {
+        $table  = new \Doctrine\DBAL\Schema\Table('autoinc_table_notnull_enabled');
+        $column = $table->addColumn('id', $type);
+        $column->setAutoIncrement(true);
+        $column->setNotNull(true);
+
+        $sql = $this->_platform->getCreateTableSQL($table);
+
+        self::assertEquals(["CREATE TABLE autoinc_table_notnull_enabled (id $definition NOT NULL)"], $sql);
+    }
+
+    /**
+     * @dataProvider serialTypes
+     * @group 2906
+     */
+    public function testGetDefaultValueDeclarationSQLIgnoresTheDefaultKeyWhenTheFieldIsSerial(string $type) : void
+    {
+        $sql = $this->_platform->getDefaultValueDeclarationSQL(
+            [
+                'autoincrement' => true,
+                'type'          => Type::getType($type),
+                'default'       => 1,
+            ]
+        );
+
+        self::assertSame('', $sql);
+    }
+
     public function testGeneratesTypeDeclarationForIntegers()
     {
         $this->assertEquals(