Uncaught TypeError: call_user_func_array(): Argument #1 ($function) must be a valid callback – SEO

Here are some examples of callback functions that do not use anonymous functions, with PHPUnit tests.

<?php

namespace AppCalculator;

class SimpleAddition
{
    protected $operands = [];

    public function setOperands(array $operands)
    {
        $this->operands = $operands;
    }

    function  callThisOne($a, $b){
        return $a + $b;
    }

    function returnCallThisTwo(){
        $callThis = function ($a, $b){
            return $a + $b;
        };
        return $callThis;
    }    

    public function callbackMethodOne()
    {                
        $callable = array($this, 'callThisOne');
        return array_reduce($this->operands, $callable, null);
    }

    public function callbackMethodTwo()
    {        
        $callable = $this->returnCallThisTwo();
        return array_reduce($this->operands, $callable, null);
    }

    public function callbackMethodThree()
    {
        $callable = function ($a, $b){
            return $a + $b;
        };
        return array_reduce($this->operands, $callable, null);
    }

}
?>

Here’s the unit tests:

<?php

namespace TestsUnit;

use PHPUnitFrameworkTestCase;
use AppCalculatorExceptonsNoOperandsException;

class SimpleAdditionTest extends TestCase
{
    /**
     * This will test the SimpleAddition class
     *
     * @return void
     */
    public function test_addition_with_callback_method_one()
    {
        $mathObject = new AppCalculatorSimpleAddition;
        $mathObject->setOperands([2,2]);
        $this->assertEquals(4, $mathObject->callbackMethodOne());
    }

    public function test_addition_with_callback_method_two()
    {
        $mathObject = new AppCalculatorSimpleAddition;
        $mathObject->setOperands([2,2]);
        $this->assertEquals(4, $mathObject->callbackMethodTwo());
    }

    public function test_addition_with_callback_method_three()
    {
        $mathObject = new AppCalculatorSimpleAddition;
        $mathObject->setOperands([2,2]);
        $this->assertEquals(4, $mathObject->callbackMethodThree());
    }

}