Writing code to be tested

EasyToTest.php

<?php

namespace App\Components\Example;

class EasyToTest extends Sample
{
    public function __construct(
        NestedObjectA $nestedObjectA,
        NestedObjectB $nestedObjectB
    ) {
        $this->nestedObjectA = $nestedObjectA;
        $this->nestedObjectB = $nestedObjectB;
    }
}

HardToTest.php

<?php

namespace App\Components\Example;

class HardToTest extends Sample
{
    public function __construct()
    {
        $this->nestedObjectA = new NestedObjectA();
        $this->nestedObjectB = new NestedObjectB(
            $this->nestedObjectA
        );
    }
}

NestedObjectA.php

<?php

namespace App\Components\Example;

class NestedObjectA
{
    private $i = 1;

    public function foo()
    {
        $this->i++;
    }

    public function bar()
    {
        return $this->i--;
    }
}

NestedObjectB.php

<?php

namespace App\Components\Example;

class NestedObjectB
{
    private $nestObjectA;

    public function __construct(NestedObjectA $nestedObjectA)
    {
        $this->nestObjectA = $nestedObjectA;
    }

    public function foobar()
    {
        $this->nestObjectA->foo();
        return $this->nestObjectA->bar();
    }
}

Sample.php

<?php

namespace App\Components\Example;

class Sample
{
    /**
     * @var NestedObjectA
     */
    protected $nestedObjectA;

    /**
     * @var NestedObjectB
     */
    protected $nestedObjectB;

    public function doSomething()
    {
        return $this->nestedObjectA->bar() + 2;
    }

    public function doSomethingElse()
    {
        return $this->nestedObjectB->foobar();
    }
}

TestingSamples.php

<?php

use App\Components\Example\EasyToTest;
use App\Components\Example\HardToTest;
use App\Components\Example\NestedObjectA;
use App\Components\Example\NestedObjectB;
use PHPUnit\Framework\TestCase;

class TestingSamples extends TestCase
{
    /**
     * @var NestedObjectA
     */
    private $nestedObjectAMock;

    /**
     * @var NestedObjectB
     */
    private $nestedObjectBMock;

    public function setup()
    {
        $this->nestedObjectAMock = $this->getMockBuilder(
            NestedObjectA::class
        )
            ->disableOriginalConstructor()
            ->getMock();

        $this->nestedObjectBMock = $this->getMockBuilder(
            NestedObjectB::class
        )
            ->disableOriginalConstructor()
            ->getMock();
    }

    /**
     * @test
     */
    public function testHardToTest()
    {
        $hardToTest = new HardToTest();

        $this->assertEquals(
            3,
            $hardToTest->doSomething(),
            "Returning value does not equal 3"
        );
    }

    /**
     * @test
     */
    public function testDoSomethingInEasyToTest()
    {
        $easyToTest = new EasyToTest(
            $this->nestedObjectAMock,
            $this->nestedObjectBMock
        );

        $this->nestedObjectAMock
            ->expects(self::once())
            ->method('bar')
            ->with();

        $easyToTest->doSomething();
    }

    public function testDoSomethingElseInEasyToTest()
    {
        // Write me
    }

}