Tests: add a dedicated test file for the wpdb::_real_escape() method

tests/phpunit/tests/db/realEscape.php

@@ -0,0 +1,87 @@
+<?php
+
+/**
+ * Test WPDB _real_escape() method.
+ *
+ * @group  wpdb
+ * @covers wpdb::_real_escape
+ */
+class Tests_DB_RealEscape extends WP_UnitTestCase {
+
+	/**
+	 * Test that various types of input passed to `wpdb::_real_escape()` are handled correctly.
+	 *
+	 * Note: this test does not test the actual escaping or other logic in the function.
+	 * It just and only tests and documents how the function handles various input types.
+	 *
+	 * @ticket 53635
+	 *
+	 * @dataProvider data_real_escape_input_type_handling
+	 *
+	 * @param mixed  $input    The input to escape.
+	 * @param string $expected The expected function output.
+	 */
+	function test_real_escape_input_type_handling( $input, $expected ) {
+		global $wpdb;
+
+		$this->assertSame( $expected, $wpdb->_real_escape( $input ) );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @var array
+	 */
+	public function data_real_escape_input_type_handling() {
+		return array(
+			'null'             => array(
+				'input'    => null,
+				'expected' => '',
+			),
+			'boolean false'    => array(
+				'input'    => false,
+				'expected' => '',
+			),
+			'boolean true'     => array(
+				'input'    => true,
+				'expected' => '1',
+			),
+			'integer zero'     => array(
+				'input'    => 0,
+				'expected' => '0',
+			),
+			'negative integer' => array(
+				'input'    => -1327,
+				'expected' => '-1327',
+			),
+			'positive integer' => array(
+				'input'    => 47896,
+				'expected' => '47896',
+			),
+			'float zero'       => array(
+				'input'    => 0.0,
+				'expected' => '0',
+			),
+			'positive float'   => array(
+				'input'    => 25.52,
+				'expected' => '25.52',
+			),
+			'simple string'    => array(
+				'input'    => 'foobar',
+				'expected' => 'foobar',
+			),
+			'empty array'      => array(
+				'input'    => array(),
+				'expected' => '',
+			),
+			'non-empty array'  => array(
+				'input'    => array( 1, 2, 3 ),
+				'expected' => '',
+			),
+			'simple object'    => array(
+				'input'    => new stdClass(),
+				'expected' => '',
+			),
+		);
+	}
+}