Class is not found phpunit

I have written phpunit test. I ran it by using following commands:

C:\Program Files (x86)\Ampps\www\phpunit.dev\vendor\bin>phpunit -c ../../phpunit.xml

But end up having this error:

PHP Fatal error: Class 'Acme\SumFinder' not found in C:\Program Files (x86)\Ampps\www\phpunit.dev\tests\AcmeTests\SumFinderTest.php on line 15

I have tried several solutions from these questions:

• Class 'sample\question2\Hello' not found with composer and phpunit
• Autoloading classes in PHPUnit using Composer and autoload.php

but nothing works. What could be the problem and how am I going to solve it? Thanks!

My directory structures:

• phpunit.dev/src/Acme/SumFinder.php
• phpunit.dev/tests/AcmeTests/SumFinderTest.php
• phpunit.dev/composer.json
• phpunit.dev/phpunit.xml

My composer.json written like this:

{
 "require-dev": {
 "phpunit/phpunit": "3.7.*"
},
 "autoload": {
   "psr-4": {
   "Acme\\": "./src/"
 }
},
 "autoload-dev": {
  "psr-4": {
  "AcmeTests\\": "./tests/"
  }
 }
}

My Acme\SumFinder.php written like this:

<?php 
 namespace Acme;
 class SumFinder {
  private $inputArray;
  function __construct($inputArray = null) { ... }
  function findSum() { ... }
  function compareArrays() { ... }
 }
?>

My AcmeTests\SumFinderTest.php:

<?php 
  namespace AcmeTests;
  use Acme\SumFinder;

  class SumFinderTest extends \PHPUnit_Framework_TestCase
    function testFindSum() { ... }
    function testCompareArrays() { ... }
?>

My phpunit.xml config file:

<?xml version="1.0" encoding="utf-8" ?>
<phpunit colors="true" bootstrap="./vendor/autoload.php">
  <testsuites>
  <testsuite name="First Test">
    <directory>./tests</directory>
  </testsuite>
</testsuites>

I am using windows 10 and AMPPS stack if it could help solve my problem.