diff --git a/tests/phpunit/tests/date/wpCheckdate.php b/tests/phpunit/tests/date/wpCheckdate.php
new file mode 100644
index 0000000000..204489200c
--- /dev/null
+++ b/tests/phpunit/tests/date/wpCheckdate.php
@@ -0,0 +1,67 @@
+<?php
+
+/**
+ * Tests for the wp_checkdate() function.
+ *
+ * @ticket 59825
+ *
+ * @group date
+ * @group datetime
+ * @group functions
+ *
+ * @covers ::wp_checkdate
+ */
+class Tests_Date_wpCheckdate extends WP_UnitTestCase {
+
+	/**
+	 * @dataProvider data_wp_checkdate
+	 *
+	 * @param int|string $month       The month to check.
+	 * @param int|string $day         The day to check.
+	 * @param int|string $year        The year to check.
+	 * @param string     $source_date The date to pass to the wp_checkdate filter.
+	 * @param bool       $expected    The expected result.
+	 */
+	public function test_wp_checkdate( $month, $day, $year, $source_date, $expected ) {
+		$this->assertSame( $expected, wp_checkdate( $month, $day, $year, $source_date ) );
+	}
+
+	/**
+	 * Data provider for test_wp_checkdate().
+	 *
+	 * @return array
+	 */
+	public function data_wp_checkdate() {
+		return array(
+			'integers'              => array( 1, 1, 1, '1-1-1', true ),
+			'strings'               => array( '1', '1', '1', '1-1-1', true ),
+			'arbitrary source_date' => array( 1, 1, 1, 'arbitrary source_date', true ), // source_date is only used by the filter.
+			'valid day'             => array( 2, 29, 2024, '2/29/2024', true ),         // 2024 is a leap year.
+			'invalid day'           => array( 2, 29, 2023, '2/29/2023', false ),        // 2023 is not a leap year.
+			'invalid month'         => array( 99, 1, 1, '1-1-1', false ),               // Month must be between 1 and 12.
+			'invalid year'          => array( 1, 1, 0, '1-1-0', false ),                // Year must be between 1 and 32767.
+		);
+	}
+
+	/**
+	 * Checks that the filter overrides the return value.
+	 */
+	public function test_wp_checkdate_filter() {
+		add_filter(
+			'wp_checkdate',
+			static function ( $is_valid_date, $source_date ) {
+				if ( '2/29/2023' === $source_date ) {
+					// Date is invalid, but return true anyway.
+					return true;
+				}
+
+				return $is_valid_date;
+			},
+			10,
+			2
+		);
+
+		// Test with an invalid date that the filter will return as valid.
+		$this->assertTrue( wp_checkdate( '2', '29', '2023', '2/29/2023' ) );
+	}
+}