diff --git a/tests/phpunit/tests/functions/wpListFilter.php b/tests/phpunit/tests/functions/wpListFilter.php
index 1039b70f3ec20..2c9a8a7d6b134 100644
--- a/tests/phpunit/tests/functions/wpListFilter.php
+++ b/tests/phpunit/tests/functions/wpListFilter.php
@@ -10,6 +10,8 @@
 class Tests_Functions_wpListFilter extends WP_UnitTestCase {
 
 	/**
+	 * @ticket 53987
+	 *
 	 * @dataProvider data_wp_list_filter
 	 *
 	 * @param array  $input_list An array of objects to filter.
@@ -22,6 +24,32 @@ public function test_wp_list_filter( $input_list, $args, $operator, $expected )
 		$this->assertEqualSetsWithIndex( $expected, wp_list_filter( $input_list, $args, $operator ) );
 	}
 
+	/**
+	 * Tests that the 'AND' operator is used when no operator is passed.
+	 *
+	 * @ticket 53987
+	 */
+	public function test_wp_list_filter_should_default_to_and_operator() {
+		$input_list = array(
+			(object) array(
+				'foo' => 'bar',
+				'bar' => 'baz',
+			),
+			(object) array( 'foo' => 'bar' ),
+		);
+
+		$this->assertEqualSetsWithIndex(
+			array( 0 => $input_list[0] ),
+			wp_list_filter(
+				$input_list,
+				array(
+					'foo' => 'bar',
+					'bar' => 'baz',
+				)
+			)
+		);
+	}
+
 	/**
 	 * Data provider.
 	 *
@@ -29,25 +57,25 @@ public function test_wp_list_filter( $input_list, $args, $operator, $expected )
 	 */
 	public static function data_wp_list_filter() {
 		return array(
-			'string instead of array'  => array(
+			'string instead of array'                   => array(
 				'foo',
 				array(),
 				'AND',
 				array(),
 			),
-			'object instead of array'  => array(
+			'object instead of array'                   => array(
 				(object) array( 'foo' ),
 				array(),
 				'AND',
 				array(),
 			),
-			'empty args'               => array(
+			'empty args'                                => array(
 				array( 'foo', 'bar' ),
 				array(),
 				'AND',
 				array( 'foo', 'bar' ),
 			),
-			'invalid operator'         => array(
+			'invalid operator'                          => array(
 				array(
 					(object) array( 'foo' => 'bar' ),
 					(object) array( 'foo' => 'baz' ),
@@ -56,7 +84,7 @@ public static function data_wp_list_filter() {
 				'XOR',
 				array(),
 			),
-			'single argument to match' => array(
+			'single argument to match'                  => array(
 				array(
 					(object) array(
 						'foo' => 'bar',
@@ -94,7 +122,7 @@ public static function data_wp_list_filter() {
 					),
 				),
 			),
-			'all must match'           => array(
+			'all must match'                            => array(
 				array(
 					(object) array(
 						'foo' => 'bar',
@@ -132,7 +160,7 @@ public static function data_wp_list_filter() {
 					),
 				),
 			),
-			'any must match'           => array(
+			'any must match'                            => array(
 				array(
 					(object) array(
 						'foo' => 'bar',
@@ -179,7 +207,7 @@ public static function data_wp_list_filter() {
 					),
 				),
 			),
-			'none must match'          => array(
+			'none must match'                           => array(
 				array(
 					(object) array(
 						'foo' => 'bar',
@@ -216,7 +244,7 @@ public static function data_wp_list_filter() {
 					),
 				),
 			),
-			'string to int comparison' => array(
+			'string to int comparison'                  => array(
 				array(
 					(object) array(
 						'foo' => '1',
@@ -230,6 +258,248 @@ public static function data_wp_list_filter() {
 					),
 				),
 			),
+			'bool to string comparison'                 => array(
+				array(
+					(object) array(
+						'foo' => true,
+					),
+				),
+				array( 'foo' => 'yes' ),
+				'AND',
+				array(
+					0 => (object) array(
+						'foo' => true,
+					),
+				),
+			),
+			'null instead of array'                     => array(
+				null,
+				array( 'foo' => 'bar' ),
+				'AND',
+				array(),
+			),
+			'empty list'                                => array(
+				array(),
+				array( 'foo' => 'bar' ),
+				'AND',
+				array(),
+			),
+
+			/*
+			 * Empty arguments are checked before the operator is validated,
+			 * so the original list is returned even for an invalid operator.
+			 */
+			'empty args, invalid operator'              => array(
+				array( 'foo', 'bar' ),
+				array(),
+				'XOR',
+				array( 'foo', 'bar' ),
+			),
+
+			// The operator is uppercased before it is validated.
+			'lowercase AND operator'                    => array(
+				array(
+					(object) array( 'foo' => 'bar' ),
+					(object) array( 'foo' => 'baz' ),
+				),
+				array( 'foo' => 'bar' ),
+				'and',
+				array(
+					0 => (object) array( 'foo' => 'bar' ),
+				),
+			),
+			'mixed case OR operator'                    => array(
+				array(
+					(object) array( 'foo' => 'bar' ),
+					(object) array( 'foo' => 'baz' ),
+				),
+				array( 'foo' => 'bar' ),
+				'oR',
+				array(
+					0 => (object) array( 'foo' => 'bar' ),
+				),
+			),
+			'lowercase NOT operator'                    => array(
+				array(
+					(object) array( 'foo' => 'bar' ),
+					(object) array( 'foo' => 'baz' ),
+				),
+				array( 'foo' => 'bar' ),
+				'not',
+				array(
+					1 => (object) array( 'foo' => 'baz' ),
+				),
+			),
+
+			// Lists of arrays are supported alongside lists of objects.
+			'arrays: single argument to match'          => array(
+				array(
+					array(
+						'foo' => 'bar',
+						'key' => 'foo',
+					),
+					array(
+						'foo' => 'baz',
+						'key' => 'value',
+					),
+					array(
+						'foo' => 'bar',
+						'key' => 'value',
+					),
+				),
+				array( 'foo' => 'bar' ),
+				'AND',
+				array(
+					0 => array(
+						'foo' => 'bar',
+						'key' => 'foo',
+					),
+					2 => array(
+						'foo' => 'bar',
+						'key' => 'value',
+					),
+				),
+			),
+			'arrays: all must match'                    => array(
+				array(
+					array(
+						'foo' => 'bar',
+						'bar' => 'baz',
+					),
+					array( 'foo' => 'bar' ),
+				),
+				array(
+					'foo' => 'bar',
+					'bar' => 'baz',
+				),
+				'AND',
+				array(
+					0 => array(
+						'foo' => 'bar',
+						'bar' => 'baz',
+					),
+				),
+			),
+			'arrays: any must match'                    => array(
+				array(
+					array( 'foo' => 'bar' ),
+					array( 'bar' => 'baz' ),
+					array( 'foo' => 'baz' ),
+				),
+				array(
+					'foo' => 'bar',
+					'bar' => 'baz',
+				),
+				'OR',
+				array(
+					0 => array( 'foo' => 'bar' ),
+					1 => array( 'bar' => 'baz' ),
+				),
+			),
+			'arrays: none must match'                   => array(
+				array(
+					array( 'foo' => 'bar' ),
+					array( 'bar' => 'baz' ),
+					array( 'foo' => 'baz' ),
+				),
+				array(
+					'foo' => 'bar',
+					'bar' => 'baz',
+				),
+				'NOT',
+				array(
+					2 => array( 'foo' => 'baz' ),
+				),
+			),
+			'mixed arrays and objects'                  => array(
+				array(
+					array( 'foo' => 'bar' ),
+					(object) array( 'foo' => 'bar' ),
+					array( 'foo' => 'baz' ),
+					(object) array( 'foo' => 'baz' ),
+				),
+				array( 'foo' => 'bar' ),
+				'AND',
+				array(
+					0 => array( 'foo' => 'bar' ),
+					1 => (object) array( 'foo' => 'bar' ),
+				),
+			),
+
+			/*
+			 * Values that are neither arrays nor objects can never match,
+			 * so they are only returned by the 'NOT' operator.
+			 */
+			'scalar values with AND'                    => array(
+				array( 'a string', 42, null, array( 'foo' => 'bar' ) ),
+				array( 'foo' => 'bar' ),
+				'AND',
+				array(
+					3 => array( 'foo' => 'bar' ),
+				),
+			),
+			'scalar values with NOT'                    => array(
+				array( 'a string', 42, null, array( 'foo' => 'bar' ) ),
+				array( 'foo' => 'bar' ),
+				'NOT',
+				array(
+					0 => 'a string',
+					1 => 42,
+					2 => null,
+				),
+			),
+
+			/*
+			 * Array values are checked with array_key_exists(), so a null value
+			 * matches, while object properties are checked with isset(),
+			 * so a null property does not.
+			 */
+			'array with a null value matching null'     => array(
+				array( array( 'foo' => null ) ),
+				array( 'foo' => null ),
+				'AND',
+				array(
+					0 => array( 'foo' => null ),
+				),
+			),
+			'object with a null property matching null' => array(
+				array( (object) array( 'foo' => null ) ),
+				array( 'foo' => null ),
+				'AND',
+				array(),
+			),
+
+			'string keys are preserved'                 => array(
+				array(
+					'first'  => (object) array( 'foo' => 'bar' ),
+					'second' => (object) array( 'foo' => 'baz' ),
+					'third'  => (object) array( 'foo' => 'bar' ),
+				),
+				array( 'foo' => 'bar' ),
+				'AND',
+				array(
+					'first' => (object) array( 'foo' => 'bar' ),
+					'third' => (object) array( 'foo' => 'bar' ),
+				),
+			),
+			'no matches with OR'                        => array(
+				array(
+					(object) array( 'foo' => 'baz' ),
+					(object) array( 'foo' => 'qux' ),
+				),
+				array( 'foo' => 'bar' ),
+				'OR',
+				array(),
+			),
+			'all matches with NOT'                      => array(
+				array(
+					(object) array( 'foo' => 'bar' ),
+					(object) array( 'foo' => 'bar' ),
+				),
+				array( 'foo' => 'bar' ),
+				'NOT',
+				array(),
+			),
 		);
 	}
 }