Run unit tests with Phpunit in lumen

Hi, I have a project of lumen with the file phpunit that comes by default that is just like this one

<?xml version="1.0" encoding="UTF-8"?>
<phpunit backupGlobals="false"
     backupStaticAttributes="false"
     bootstrap="bootstrap/app.php"
     colors="true"
     convertErrorsToExceptions="true"
     convertNoticesToExceptions="true"
     convertWarningsToExceptions="true"
     processIsolation="false"
     stopOnFailure="false"
     syntaxCheck="false">
<testsuites>
    <testsuite name="Application Test Suite">
        <directory suffix="Test.php">./tests</directory>
    </testsuite>
</testsuites>
<filter>
    <whitelist processUncoveredFilesFromWhitelist="true">
        <directory suffix=".php">./app</directory>
    </whitelist>
</filter>
<php>
    <env name="APP_ENV" value="testing"/>
    <env name="CACHE_DRIVER" value="array"/>
    <env name="QUEUE_DRIVER" value="sync"/>
</php>

The file .env I have it this way

APP_ENV=local
APP_DEBUG=true
APP_KEY=
APP_TIMEZONE=UTC

Now I go to the console and I execute phpunit from the project directory and what I receive by screen is the following

PHPUnit 5.4.6 by Sebastian Bergmann and contributors.

  

Time: 37 ms, Memory: 8.00MB

     

No tests executed!

If I look at the test folder I see the following files

edu@pc1:/var/www/html/proyecto1/tests$ ls -alh
total 20K
drwxr-xr-x  2 edu edu 4,0K feb 28 13:40 .
drwxr-xr-x 14 edu edu 4,0K feb 28 13:23 ..
-rwxr-xr-x  1 edu edu  390 feb 16 16:53 ExampleTest.php
-rwxr-xr-x  1 edu edu  279 feb 16 16:53 TestCase.php
-rwxr-xr-x  1 edu edu  324 feb 28 13:35 UserTest.php
edu@pc1:/var/www/html/proyecto1/tests$ 

I've also tried running phpunit of a single file and I get this error:

  

edu @ pc1: / var / www / html / project1 $ phpunit tests / TestCase.php   Class 'tests / TestCase' could not be found in '/var/www/html/project1/tests/TestCase.php'.