How to test if string contains another string in PHPUnit?

As you could tell assertContains is for checking that an array contains a value.

Looking to see if the string contains a substring, your simplest query would be to use assertRegexp()

$this->assertRegexp('/flour/', $plaintext);

You would just need to add the delimiters.

If you really want to have an assertStringContains assertion, you can extend PHPUnit_Framework_TestCase and create your own.

UPDATE

In the latest version of PHPUnit, assertContains will work on strings.

You can always hide the ugliness inside a custom assertion method, so basically I would have a BaseTestCase class which inherits from the phpunit test case which you could use to have your own library of reusable assertions (see http://xunitpatterns.com/Custom%20Assertion.html).. (In php 5.4 you can use traits as well, imho assertion libraries are one of the cases where traits actually are useful)..I always introduce quite a few custom assertions in my projects, often domain specific. And yes, some are ugly too:) well, I guess that's what encapsulation is there for... Amongst things...:)

UPDATE: I just checked and 'assertContains' and 'assertNotContains' actually also operate on strings as well as arrays (and anything that implements 'Traversable'):

function test_Contains()
{
    $this->assertContains("test", "this is a test string" );
    $this->assertNotContains("tst", "this is a test string");
}

2019 and PHPUnit 8.0 update

assertContains() is deprecated since PHPUnit 8.0, see issue #3425.

Now the specific method is recommended (see issue #3422):

$plaintext = 'I fell on the flour';
$this->assertStringContainsString('flour', $plaintext);

TIP: Upgrade instantly with Rector and PHPUnit 8.0 set.