composer require phpunit/phpunit

 1|<?xml version="1.0" encoding="UTF-8"?>
 2|<phpunit backupGlobals="false"
 3|         backupStaticAttributes="false"
 4|         bootstrap="./config/loader.php"
 5|         colors="true"
 6|         convertErrorsToExceptions="true"
 7|         convertNoticesToExceptions="true"
 8|         convertWarningsToExceptions="true"
 9|         processIsolation="false"
10|         stopOnFailure="false">
11|    <testsuites>
12|        <testsuite name="Application Test Suite">
13|            <directory suffix="Test.php">./tests</directory>
14|        </testsuite>
15|    </testsuites>
16|    <logging>
17|        <log type="coverage-html" target="./phpunit_report" charset="UTF-8"
18|             yui="true" highlight="true"
19|             lowUpperBound="50" highLowerBound="80" />
20|    </logging>
21|    <filter>
22|        <whitelist processUncoveredFilesFromWhitelist="true">
23|            <directory suffix=".php">./app</directory>
24|            <exclude>
25|
26|            </exclude>
27|        </whitelist>
28|    </filter>
29|    <php>
30|        <env name="APP_MODE" value="testing"/>
31|    </php>
32|</phpunit>

<?php

// tests/UtilCase.php

use App\Providers\Util;

class UtilTest extends TestCase
{
        public function testCamelToUnderScore()
        {
                $data = 'abcDeFGhiJk';
                $this->assertTrue(Util::camelCaseToUnderScore($data) === 'abc_de_fghi_jk');
        }
}

./vender/bin/phpunit

./tests/*Test.php

public function test*()
{
    //...test code
}

public function test*()
{
    //...test code
}

public function test*()
{
    //...test code
}

Load phpunit.xml