diff --git a/tests/phpunit/tests/dbdelta.php b/tests/phpunit/tests/dbdelta.php
index 6cdc325dab..7dbb96abcf 100755
--- a/tests/phpunit/tests/dbdelta.php
+++ b/tests/phpunit/tests/dbdelta.php
@@ -8,16 +8,260 @@
  */
 class Tests_dbDelta extends WP_UnitTestCase {
 
-	function test_create_new_table() {
-		include_once( ABSPATH . 'wp-admin/includes/upgrade.php');
-		$table_name = 'test_new_table';
+	/**
+	 * Make sure the upgrade code is loaded before the tests are run.
+	 */
+	public static function setUpBeforeClass() {
 
-		$create = "CREATE TABLE $table_name (\n a varchar(255)\n)";
-		$expected = array( $table_name => "Created table $table_name" );
+		parent::setUpBeforeClass();
 
-		$actual = dbDelta( $create, false );
+		require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
+	}
 
-		$this->assertSame( $expected, $actual );
+	/**
+	 * Create a custom table to be used in each test.
+	 */
+	public function setUp() {
+
+		global $wpdb;
+
+		$wpdb->query(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compoud_key (id,column_1)
+			)
+			"
+		);
+
+		parent::setUp();
+	}
+
+	/**
+	 * Delete the custom table on teardown.
+	 */
+	public function tearDown() {
+
+		global $wpdb;
+
+		parent::tearDown();
+
+		$wpdb->query( "DROP TABLE IF EXISTS {$wpdb->prefix}dbdelta_test" );
+	}
+
+	/**
+	 * Test table creation.
+	 */
+	public function test_creating_a_table() {
+
+		remove_filter( 'query', array( $this, '_create_temporary_tables' ) );
+		remove_filter( 'query', array( $this, '_drop_temporary_tables' ) );
+
+		global $wpdb;
+
+		$updates = dbDelta(
+			"CREATE TABLE {$wpdb->prefix}dbdelta_create_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				PRIMARY KEY  (id)
+			);"
+		);
+
+		$expected = array(
+			"{$wpdb->prefix}dbdelta_create_test" => "Created table {$wpdb->prefix}dbdelta_create_test"
+		);
+
+		$this->assertEquals( $expected, $updates );
+
+		$this->assertEquals(
+			"{$wpdb->prefix}dbdelta_create_test"
+			, $wpdb->get_var(
+				$wpdb->prepare(
+					'SHOW TABLES LIKE %s'
+					, $wpdb->esc_like( "{$wpdb->prefix}dbdelta_create_test" )
+				)
+			)
+		);
+
+		$wpdb->query( "DROP TABLE {$wpdb->prefix}dbdelta_create_test" );
+	}
+
+	/**
+	 * Test that it does nothing for an existing table.
+	 */
+	public function test_existing_table() {
+
+		global $wpdb;
+
+		$updates = dbDelta(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compoud_key (id,column_1)
+			)
+			"
+		);
+
+		$this->assertEquals( array(), $updates );
+	}
+
+	/**
+	 * Test the column type is updated.
+	 */
+	public function test_column_type_change() {
+
+		global $wpdb;
+
+		// id: bigint(20) => int(11)
+		$updates = dbDelta(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id int(11) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compoud_key (id,column_1)
+			)
+			"
+		);
+
+		$this->assertEquals(
+			array(
+				"{$wpdb->prefix}dbdelta_test.id"
+					=> "Changed type of {$wpdb->prefix}dbdelta_test.id from bigint(20) to int(11)"
+			)
+			, $updates
+		);
+	}
+
+	/**
+	 * Test new column added.
+	 */
+	public function test_column_added() {
+
+		global $wpdb;
+
+		$updates = dbDelta(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				extra_col longtext,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compoud_key (id,column_1)
+			)
+			"
+		);
+
+		$this->assertEquals(
+			array(
+				"{$wpdb->prefix}dbdelta_test.extra_col"
+					=> "Added column {$wpdb->prefix}dbdelta_test.extra_col"
+			)
+			, $updates
+		);
+
+		$this->assertTableHasColumn( 'column_1', $wpdb->prefix . 'dbdelta_test' );
+	}
+
+	/**
+	 * Test that it does nothing when a column is removed.
+	 *
+	 * @ticket 26801
+	 */
+	public function test_columns_arent_removed() {
+
+		global $wpdb;
+
+		// No column column_1
+		$updates = dbDelta(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compoud_key (id,column_1)
+			)
+			"
+		);
+
+		$this->assertEquals( array(), $updates );
+
+		$this->assertTableHasColumn( 'column_1', $wpdb->prefix . 'dbdelta_test' );
+	}
+
+	/**
+	 * Test that nothing happens with $execute is false.
+	 */
+	public function test_no_execution() {
+
+		global $wpdb;
+
+		// Added column extra_col
+		$updates = dbDelta(
+			"
+			CREATE TABLE {$wpdb->prefix}dbdelta_test (
+				id bigint(20) NOT NULL AUTO_INCREMENT,
+				column_1 varchar(255) NOT NULL,
+				extra_col longtext,
+				PRIMARY KEY  (id),
+				KEY key_1 (column_1),
+				KEY compoud_key (id,column_1)
+			)
+			"
+			, false // Don't execute.
+		);
+
+		$this->assertEquals(
+			array(
+				"{$wpdb->prefix}dbdelta_test.extra_col"
+					=> "Added column {$wpdb->prefix}dbdelta_test.extra_col"
+			)
+			, $updates
+		);
+
+		$this->assertTableHasNotColumn( 'extra_col', $wpdb->prefix . 'dbdelta_test' );
+	}
+
+	//
+	// Assertions.
+	//
+
+	/**
+	 * Assert that a table has a column.
+	 *
+	 * @param string $column The field name.
+	 * @param string $table  The database table name.
+	 */
+	protected function assertTableHasColumn( $column, $table ) {
+
+		global $wpdb;
+
+		$table_fields = $wpdb->get_results( "DESCRIBE {$table}" );
+
+		$this->assertCount( 1, wp_list_filter( $table_fields, array( 'Field' => $column ) ) );
+	}
+
+	/**
+	 * Assert that a table doesn't have a column.
+	 *
+	 * @param string $column The field name.
+	 * @param string $table  The database table name.
+	 */
+	protected function assertTableHasNotColumn( $column, $table ) {
+
+		global $wpdb;
+
+		$table_fields = $wpdb->get_results( "DESCRIBE {$table}" );
+
+		$this->assertCount( 0, wp_list_filter( $table_fields, array( 'Field' => $column ) ) );
 	}
 
 	/**
@@ -30,7 +274,6 @@ class Tests_dbDelta extends WP_UnitTestCase {
 			$this->markTestSkipped( 'This test requires utf8mb4 support in MySQL.' );
 		}
 
-		include_once( ABSPATH . 'wp-admin/includes/upgrade.php');
 		$table_name = 'test_truncated_index';
 
 		$create = "CREATE TABLE $table_name (\n a varchar(255) COLLATE utf8mb4_unicode_ci,\n KEY a (a)\n)";