MDL-81074 core: Add assertTimeStringMatches PHPUnit Assertion

Also raised as sebastianbergmann/phpunit#5757

lib/phpunit/classes/base_testcase.php

@@ -121,6 +121,30 @@ public static function assertValidKeys(array $hash, array $validKeys) {
         return $hash;
     }
 
+    /**
+     * Assert that two Date/Time strings are equal.
+     *
+     * The strings generated by \DateTime, \strtotime, \date, \time, etc. are generated outside of our control.
+     * From time-to-time string changes are made.
+     * One such example is from ICU 72.1 which changed the time format to include a narrow-non-breaking-space (U+202F)
+     * between the time and AM/PM.
+     *
+     * We should not update our tests to match these changes, as it is not our code that is generating the strings and they may change again.
+     * In addition the changes are not equal amongst all systems as they depend on the version of ICU installed.
+     *
+     * @param string $expected
+     * @param string $actual
+     * @param ?string $message
+     */
+    public function assertEqualsIgnoringWhitespace($expected, $actual, string $message = '') {
+        // ICU 72.1 introduced the use of a narrow-non-breaking-space (U+202F) between the time and the AM/PM.
+        // Normalise all whitespace when performing the comparison.
+        $expected = preg_replace('/\s+/u', ' ', $expected);
+        $actual = preg_replace('/\s+/u', ' ', $actual);
+
+        $this->assertEquals($expected, $actual, $message);
+    }
+
     /**
      * Parse out the options from the tag using DOM object tree.
      *