test(Generators): add string cmd test

- Add a test that checks if the `processHelperRun` method successfully runs a string command.
- The test uses the `echo` command to output the string 'foo' and     expects the command to be successful.
- The test is grouped under the directory and file where it is located.

tests/Unit/Generators/GeneratorTest.php

@@ -26,6 +26,10 @@
  $this->generator = $generator;
 });
 
+it('can run string cmd', function (): void {
+ expect($this->generator->processHelperRun('echo foo'))->isSuccessful()->toBeTrue();
+})->group(__DIR__, __FILE__);
+
 it('can sanitize output to JSON', function (): void {
  $output = <<<'OUTPUT'
  {