Index: tests/phpunit/tests/option/registration.php
===================================================================
--- tests/phpunit/tests/option/registration.php	(revision 0)
+++ tests/phpunit/tests/option/registration.php	(working copy)
@@ -0,0 +1,55 @@
+<?php
+
+/**
+ * @group option
+ */
+class Tests_Option_Registration extends WP_UnitTestCase {
+	public function test_register() {
+		register_setting( 'test_group', 'test_option' );
+
+		$registered = get_registered_settings();
+		$this->assertArrayHasKey( 'test_option', $registered );
+
+		$args = $registered['test_option'];
+		$this->assertEquals( 'test_group', $args['group'] );
+
+		// Check defaults.
+		$this->assertEquals( 'string', $args['type'] );
+		$this->assertEquals( false, $args['show_in_rest'] );
+		$this->assertEquals( '', $args['description'] );
+	}
+
+	public function test_register_with_callback() {
+		register_setting( 'test_group', 'test_option', array( $this, 'filter_registered_setting' ) );
+
+		$filtered = apply_filters( 'sanitize_option_test_option', 'smart', 'test_option', 'smart' );
+		$this->assertEquals( 'S-M-R-T', $filtered );
+	}
+
+	public function test_register_with_array() {
+		register_setting( 'test_group', 'test_option', array(
+			'sanitize_callback' => array( $this, 'filter_registered_setting' ),
+		));
+
+		$filtered = apply_filters( 'sanitize_option_test_option', 'smart', 'test_option', 'smart' );
+		$this->assertEquals( 'S-M-R-T', $filtered );
+	}
+
+	public function filter_registered_setting() {
+		return 'S-M-R-T';
+	}
+
+	/**
+	 * @expectedDeprecated register_setting
+	 */
+	public function test_register_deprecated_group_misc() {
+		register_setting( 'misc', 'test_option' );
+	}
+
+	/**
+	 * @expectedDeprecated register_setting
+	 */
+	public function test_register_deprecated_group_privacy() {
+		register_setting( 'privacy', 'test_option' );
+	}
+}