Cakephp 3 unit test unable to post data - unit-testing

Question

I run an api using postman, it works. But my unit tests that I create for it doesn't work
Below is my unit test file
<?php
namespace App\Test\TestCase\Controller\Api;
use App\Controller\Api\EmployeesController;
use Cake\TestSuite\IntegrationTestCase;
/**
* App\Controller\Api\EmployeesController Test Case
*/
class EmployeesApiControllerTest extends IntegrationTestCase
{
/**
* Fixtures
*
* #var array
*/
public $fixtures = [
'app.projects',
'app.projects_sites',
'app.transactions',
'app.sites'
];
/**
* Test REST API PIN login
*/
public function testJwtToken() {
$this->configRequest([
'headers' => [
'Accept' => 'application/json',
'Content-Type' => 'application/json'
]
]);
$this->post('/api/employees/token', ['pin_code' => '1001']);
$this->assertResponseOk();
}
}
And this is the console response after running it
$ docker-compose run webapp vendor/bin/phpunit tests/TestCase/Controller/Api/EmployeesApiControllerTest.php
Starting timesheetcakephp_mysql_1 ... done
PHPUnit 6.5.7 by Sebastian Bergmann and contributors.
F 1 / 1 (100%)
Time: 1.52 seconds, Memory: 6.00MB
There was 1 failure:
1) App\Test\TestCase\Controller\Api\EmployeesApiControllerTest::testJwtToken
Status code is not between 200 and 204
Failed asserting that 500 is equal to 204 or is less than 204.
/var/www/html/vendor/cakephp/cakephp/src/TestSuite/IntegrationTestCase.php:796
/var/www/html/vendor/cakephp/cakephp/src/TestSuite/IntegrationTestCase.php:713
/var/www/html/tests/TestCase/Controller/Api/EmployeesApiControllerTest.php:37
FAILURES!
Tests: 1, Assertions: 4, Failures: 1.
The debug log keeps showing this
2018-03-29 19:47:13 Debug: duration=0 rows=0 SELECT Employees.id AS `Employees__id`, Employees.project_id AS `Employees__project_id`, Employees.name AS `Employees__name` FROM employees Employees WHERE Employees.pin_code = NULL LIMIT 1
I don't understand why the pin_code keep stating as NULL when I have clearly stated in my unit test to be '1001'.