Continuation of WordPress#4664

With tests

tests/phpunit/tests/block-supports/shadow.php

@@ -0,0 +1,89 @@
+<?php
+/**
+ * @group block-supports
+ *
+ * @covers ::wp_apply_shadow_support
+ */
+class Test_Block_Supports_Shadow extends WP_UnitTestCase {
+	/**
+	 * @var string|null
+	 */
+	private $test_block_name;
+
+	public function set_up() {
+		parent::set_up();
+		$this->test_block_name = null;
+	}
+
+	public function tear_down() {
+		unregister_block_type( $this->test_block_name );
+		$this->test_block_name = null;
+		parent::set_up();
+	}
+
+	/**
+	 * @ticket 58590
+	 */
+	public function test_shadow_style_is_applied() {
+		$this->test_block_name = 'test/shadow-style-is-applied';
+		register_block_type(
+			$this->test_block_name,
+			array(
+				'api_version' => 3,
+				'attributes'  => array(
+					'style' => array(
+						'type' => 'object',
+					),
+				),
+				'supports'    => array(
+					'shadow' => true,
+				),
+			)
+		);
+		$registry   = WP_Block_Type_Registry::get_instance();
+		$block_type = $registry->get_registered( $this->test_block_name );
+		$block_atts = array(
+			'style' => array(
+				'shadow' => '60px -16px teal',
+			),
+		);
+
+		$actual   = wp_apply_shadow_support( $block_type, $block_atts );
+		$expected = array(
+			'style' => 'box-shadow:60px -16px teal;',
+		);
+
+		$this->assertSame( $expected, $actual );
+	}
+
+	/**
+	 * @ticket 58590
+	 */
+	public function test_shadow_without_block_supports() {
+		$this->test_block_name = 'test/shadow-with-skipped-serialization-block-supports';
+		register_block_type(
+			$this->test_block_name,
+			array(
+				'api_version' => 2,
+				'attributes'  => array(
+					'style' => array(
+						'type' => 'object',
+					),
+				),
+				'supports'    => array(),
+			)
+		);
+		$registry   = WP_Block_Type_Registry::get_instance();
+		$block_type = $registry->get_registered( $this->test_block_name );
+		$block_atts = array(
+			'style' => array(
+				'shadow' => '60px -16px teal',
+			),
+		);
+
+		$actual   = wp_apply_spacing_support( $block_type, $block_atts );
+		$expected = array();
+
+		$this->assertSame( $expected, $actual );
+	}
+}

tests/phpunit/tests/style-engine/styleEngine.php

@@ -26,6 +26,7 @@ public function tear_down() {
 	 *
 	 * @ticket 56467
 	 * @ticket 58549
+	 * @ticket 58590
 	 *
 	 * @covers ::wp_style_engine_get_styles
 	 *