diff --git tests/phpunit/tests/formatting/MapDeep.php tests/phpunit/tests/formatting/MapDeep.php
new file mode 100644
index 0000000..7ed88fe
--- /dev/null
+++ tests/phpunit/tests/formatting/MapDeep.php
@@ -0,0 +1,63 @@
+<?php
+/**
+ * @group formatting
+ * @ticket 22300
+ */
+class Tests_Formatting_MapDeep extends WP_UnitTestCase {
+	function setUp() {
+		if ( ! function_exists( 'map_deep' ) ) {
+			$this->markTestSkipped( "map_deep function doesn't exist" );
+		}
+
+		parent::setUp();
+	}
+
+	function test_map_deep_with_any_function_over_empty_array_should_return_empty_array() {
+		$this->assertEquals( array(), map_deep( array( $this, 'return_baba' ), array() ) );
+	}
+
+	function test_map_deep_should_map_each_element_of_array_one_level_deep() {
+		$this->assertEquals( array( 'ababa', 'xbaba' ), map_deep( array( $this, 'append_baba' ), array( 'a', 'x' ) ) );
+	}
+
+	function test_map_deep_should_map_each_element_of_array_two_levels_deep() {
+		$this->assertEquals( array( 'ababa', array( 'xbaba' ) ), map_deep( array( $this, 'append_baba' ), array( 'a', array( 'x' ) ) ) );
+	}
+
+	function test_map_deep_should_map_each_object_element_of_an_array() {
+		$this->assertEquals( array( 'var0' => 'ababa', 'var1' => (object)array( 'xbaba' ) ),
+			map_deep( array( $this, 'append_baba' ), array( 'var0' => 'a', 'var1' => (object)array( 'x' ) ) ) );
+	}
+
+	function test_map_deep_should_apply_the_function_to_a_string() {
+		$this->assertEquals( 'xbaba', map_deep( array( $this, 'append_baba' ), 'x' ) );
+	}
+
+	function test_map_deep_should_apply_the_function_to_an_integer() {
+		$this->assertEquals( '5baba' , map_deep( array( $this, 'append_baba' ), 5 ) );
+	}
+
+	function test_map_deep_should_map_each_property_of_an_object() {
+		$this->assertEquals( (object)array( 'var0' => 'ababa', 'var1' => 'xbaba' ),
+			map_deep( array( $this, 'append_baba' ), (object)array( 'var0' => 'a', 'var1' => 'x' ) ) );
+	}
+
+	function test_map_deep_should_map_each_array_property_of_an_object() {
+		$this->assertEquals( (object)array( 'var0' => 'ababa', 'var1' => array( 'xbaba' ) ),
+			map_deep( array( $this, 'append_baba' ), (object)array( 'var0' => 'a', 'var1' => array( 'x' ) ) ) );
+	}
+
+	function test_map_deep_should_map_each_object_property_of_an_object() {
+		$this->assertEquals( (object)array( 'var0' => 'ababa', 'var1' => (object)array( 'xbaba' ) ),
+			map_deep( array( $this, 'append_baba' ), (object)array( 'var0' => 'a', 'var1' => (object)array( 'x' ) ) ) );
+	}
+
+	function return_baba( $value ) {
+		return 'baba';
+	}
+
+	function append_baba( $value ) {
+		return $value . 'baba';
+	}
+}
+