public function testEnvVar()
 {
     $cmd = new Command('echo "$MULTIPROCESS_SOME_VAR"');
     $cmd->setEnvVariables(['MULTIPROCESS_SOME_VAR' => 'MultiProcess-Test']);
     $cmd->runBlocking();
     $this->assertTrue($cmd->hasExecutionResult());
     $this->assertNotNull($cmd->getExecutionResult());
     $this->assertEquals($cmd->getExecutionResult()->getStderr(), '');
     $this->assertEquals($cmd->getExecutionResult()->getStdout(), 'MultiProcess-Test');
 }