<?php

use PHPUnit\Framework\TestCase;

trait MyTrait
{
    public function traitMethod(int $int) : int
    {
        return $int * 2;
    }
}

class TraitsTest extends TestCase
{
    public function testMyMethod() : void
    {
        $mock = $this->getMockBuilder('MyTrait')
            ->getMockForTrait();
        
        $this->assertSame(6, $mock->traitMethod(3));
        
        $mock2 = $this->getMockBuilder('MyTrait')
            ->setMethods(['traitMethod'])
            ->getMockForTrait();
            
        $mock2->expects($this->once())
            ->method('traitMethod')
            ->will($this->returnValue(3));
        
        $this->assertSame(3, $mock2->traitMethod(3));
    }
}

Time: 00:00.007, Memory: 18.00 MB

OK (1 test, 0 assertions)

• Testing collections in PHPUnit
• Testing an invokation order in PHPUnit
• What setMockClassName() can do for your PHPUnit mock object

PHP 8.3, Laminas MVC 3.2, Symfony 5.2, Laravel 8.28, PHPUnit 9.5, Doctrine ORM 2.8