Установку composer проводим по инструкции.

cd ~
curl -sS https://getcomposer.org/installer -o composer-setup.php
HASH=Хеш файла
php -r "if (hash_file('SHA384', 'composer-setup.php') === '$HASH') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"

По завершению - в консоли видим сообщение, что установщик скачан успешно:

Installer verified

Переходим к установке:

sudo php composer-setup.php --install-dir=/usr/local/bin --filename=composer

По окончанию видим сообщение о успешной установке:

Output
All settings correct for using Composer
Downloading...

Composer (version 2.1.9) successfully installed to: /usr/local/bin/composer
Use it: php /usr/local/bin/composer

<?xml version="1.0" encoding="UTF-8"?>
<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.5/phpunit.xsd"
         bootstrap="tests/bootstrap.php"
         cacheResultFile=".phpunit.cache/test-results"
         colors="true"
         printerClass="Sempro\PHPUnitPrettyPrinter\PrettyPrinterForPhpUnit9"
         executionOrder="random"
         forceCoversAnnotation="true"
         beStrictAboutCoversAnnotation="true"
         beStrictAboutOutputDuringTests="true"
         beStrictAboutTodoAnnotatedTests="true"
         convertDeprecationsToExceptions="true"
         failOnRisky="true"
         failOnWarning="true"
         verbose="true">

    <php>
        <ini name="memory_limit" value="-1"/>
        <ini name="display_errors" value="true"/>
    </php>

    <testsuites>
        <testsuite name="default">
            <directory suffix="Test.php">tests</directory>
            <exclude>tests/Stubs</exclude>
            <exclude>tests/Request</exclude>
            <exclude>tests/Response</exclude>
        </testsuite>
    </testsuites>

    <coverage cacheDirectory=".phpunit.cache/code-coverage"
              processUncoveredFiles="true">
        <include>
            <directory suffix=".php">classes</directory>
        </include>
    </coverage>
</phpunit>

{
    "name": "myproject/website",
    "type": "project",
    "authors": [
        {
            "name": "Andriy Kryvenko",
            "email": "krivenko.a.b@gmail.com"
        }
    ],
    "require-dev": {
        "phpunit/phpunit": "^9",
        "sempro/phpunit-pretty-print": "^1.4"
    },
    "scripts": {
        "test": "phpunit"
    }
}

Для удобства свои классы лучше размещать в каталоге local/classes, примерно в следующем виде:

/local/classes/MyProject/Product.php
/local/classes/MyProject/Rests.php

И указать в файле /local/composer.json в секции autoload путь к каталогу:

{
    "name": "myproject/website",
    "type": "project",
    "authors": [
        {
            "name": "Andriy Kryvenko",
            "email": "krivenko.a.b@gmail.com"
        }
    ],
    "require-dev": {
        "phpunit/phpunit": "^9",
        "sempro/phpunit-pretty-print": "^1.4"
    },
    "scripts": {
        "test": "phpunit"
    },
    "autoload": {
        "psr-4": {
            "": "./classes/"
        }
    }
}

<?php

namespace MyProject\Product\Requisites;

class Leftover
{
    public int $time = 0;

    /**
     * Доступное количество для данного интервала.
     * Если количество равно -1.0 - то подразумеваем, что товара неограниченное количество
     */
    public float $quantity = 0.0;

    public function __construct(int $time, float $quantity)
    {
        $this->time = $time;
        $this->quantity = $quantity;
    }

    public function isAvailable(): bool
    {
        return ($this->quantity > 0 || $this->quantity == -1.0);
    }
}

<?php

namespace MyProject\Product\Requisites\Transform;

use MyProject\Product\Requisites\Leftover;

class LeftoverTransformer
{
    /**
     * @param string $leftoversString
     * @return Leftover[]
     * Строку получаем в виде
     * 24 часа-7|до 2 дней-14|до 7 дней-22|до 15 дней-неогр
     */
    public static function transform(string $leftoversString): array
    {
        $leftovers = [];
        $intervals = explode('|', $leftoversString);
        foreach ($intervals as $v){
            $interval = explode('-', $v);
            $intervalValues = [];
            foreach ($interval as $k => $part) {
                $intervalValues[] = trim($part);
            }

            if (!empty($intervalValues[0]) && !empty($intervalValues[1])) {
                $leftovers[] = new Leftover(
                    self::getTimeFromString($intervalValues[0]),
                    self::getQuantityFromString($intervalValues[1])
                );
            }
        }

        return $leftovers;
    }

    private static function getTimeFromString(string $timeString): int
    {
        switch ($timeString) {
            case '24 часа':
                $time = 1;
                break;
            default:
                $parts = explode(' ', $timeString);
                $time = intval($parts[1]);
                break;
        }
        return $time;
    }

    private static function getQuantityFromString(string $quantityString): int
    {
        switch ($quantityString) {
            case 'неогр':
                $quantity = -1;
                break;
            default:
                $quantity = intval($quantityString);
                break;
        }
        return $quantity;
    }
}

<?php

namespace MyProject\Product\Requisites;

use PHPUnit\Framework\TestCase;

/**
 * @covers Leftover
 */
class LeftoverTest extends TestCase
{
    public function testIsAvailable(): void
    {
        $leftover = new Leftover(1, 12.0);

        $this->assertTrue($leftover->isAvailable());
    }
  
    public function testAvailableUnlimited(): void
    {
        $leftover = new Leftover(1, -1.0);

        $this->assertTrue($leftover->isAvailable());
    }

    public function testUnavailable(): void
    {
        $leftover = new Leftover(1, 0.0);

        $this->assertFalse($leftover->isAvailable());
    }
}

<?php

namespace MyProject\Product\Requisites\Transform;

use PHPUnit\Framework\TestCase;

/**
 * @covers LeftoverTransformer
 */
class LeftoverTransformerTest extends TestCase
{
    public function testEmpty(): void
    {
        $this->assertEmpty(LeftoverTransformer::transform(''));
    }

    public function testLeftoversCount(): void
    {
        $leftoverString = '24 часа-7|до 2 дней-14|до 7 дней-22|до 15 дней-неогр';
        $leftovers = LeftoverTransformer::transform($leftoverString);

        $this->assertCount(4, $leftovers);
    }

    /**
     * @param string $leftoverString
     * @param int $expectedTime
     * @param float $expectedQuantity
     * @return void
     * @dataProvider leftoversProvider
     */
    public function testLeftovers(string $leftoverString, int $expectedTime, float $expectedQuantity): void
    {
        $leftovers = LeftoverTransformer::transform($leftoverString);

        $this->assertEquals($expectedTime, $leftovers[0]->time);
        $this->assertEquals($expectedQuantity, $leftovers[0]->quantity);
    }

    public function leftoversProvider(): array
    {
        return [
            '24 часа-7' => [
                '24 часа-7',
                1, 7.0
            ],
            'до 2 дней-14' => [
                'до 2 дней-14',
                2, 14.0
            ],
            'до 7 дней-22' => [
                'до 7 дней-22',
                7, 22.0
            ],
            'до 15 дней-неогр' => [
                'до 15 дней-неогр',
                15, -1.0
            ]
        ];
    }
}