# assertNull() >[info] ## assertNull(mixed $variable[, string $message = '']) 当 `$actual` 不是 `NULL` 时报告错误，错误讯息由 `$message` 指定。 `assertNotNull()` 是与之相反的断言，接受相同的参数。 **Example A.32. assertNull() 的使用** ~~~ <?php class NullTest extends PHPUnit_Framework_TestCase { public function testFailure() { $this->assertNull('foo'); } } ?> ~~~ ~~~ phpunit NotNullTest PHPUnit 5.0.0 by Sebastian Bergmann and contributors. F Time: 0 seconds, Memory: 5.00Mb There was 1 failure: 1) NullTest::testFailure Failed asserting that 'foo' is null. /home/sb/NotNullTest.php:6 FAILURES! Tests: 1, Assertions: 1, Failures: 1. ~~~