PHPUnit | assertContainsOnly() Function

The assertContainsOnly() function is a builtin function in PHPUnit and is used to assert an array to contain all its values as the given data type. This assertion will return true in the case if the array contains values of only given data type else return false and in case of true the asserted test case got passed else test case got failed.
Syntax:

assertContainsOnly(string $dataType, array $array, 
                 boolean $isNativeType = null, string $message = '')

Parameters: This function accepts four parameters as shown in the above syntax. The parameters are described below: 

• $dataType: This parameter is a string which consists of the name of datatype.
• $array: This parameter is array for which the assert function will check whether it contains only values of given type or not.
• $isNativeType: This parameters tell whether the datatype is PHP native data type or not.
• $message: This parameter takes string value. When the testcase got failed this string message got displayed as error message.

Below programs illustrate the assertContainsOnly() function in PHPUnit:
Program 1:

php

<?php
use PHPUnit\Framework\TestCase;

class GeeksPhpunitTestCase extends TestCase
{
    public function testNegativeTestcaseForAssertContainsOnly()
    {
        $testArray = array("geeksforgeek", 2);
        $dataType = "string";
        // assert function to test whether testArray contains
        // only string values
        $this->assertContainsOnly($dataType, $testArray, null,
                 "testArray doesn't  contains only string") ;
    }
}

?>

Output:

PHPUnit 8.2.5 by Sebastian Bergmann and contributors.

F                                                                   1 / 1 (100%)

Time: 236 ms, Memory: 10.00 MB

There was 1 failure:

1) GeeksPhpunitTestCase::testNegativeTestcaseForAssertContainsOnly
testArray doesn't  contains only string
Failed asserting that Array &0 (
    0 => 'geeksforgeek'
    1 => 2
) contains only values of type "string".

/home/shivam/Documents/geeks/phpunit/abc.php:11

FAILURES!
Tests: 1, Assertions: 1, Failures: 1.

Program 2:

php

<?php
use PHPUnit\Framework\TestCase;

class GeeksPhpunitTestCase extends TestCase
{
    public function testPositiveTestcaseForAssertContainsOnly()
    {
        $testArray = array("geeksforgeek", "learn");
        $dataType = "string";
        // assert function to test whether testArray contains
        // only string values
        $this->assertContainsOnly($dataType, $testArray, null,
               "testArray doesn't  contains only string") ;
    }
}

?>

Output:

PHPUnit 8.2.5 by Sebastian Bergmann and contributors.

.                                                                   1 / 1 (100%)

Time: 67 ms, Memory: 10.00 MB

OK (1 test, 1 assertion)

Note: To run testcases with phpunit follow steps from here. Also, assertContainsOnly() is supported by phpunit 7 and above.