I'm having a problem.. My boss don't want to let...

If your inquiry relates to the employer refraining from signing the employment contract, the following information:
The UAE Labor Law stipulates that the test clause must be written in the employment contract. It is not valid for the employer to test the worker without a labor contract that includes the condition of the worker being subjected to the trial period and if the employer refuses to renew or cancel the visa, the worker can file a complaint with the General Directorate of Residence against the employer.If you are on a visit visa and have not been amended to a work visa, you cannot file a complaint with the Ministry of Human Resources and Emiratisation.
Here is the text of the UAE Labor Law regarding your inquiry:
Article 37
The worker may be appointed under probation for a period not exceeding six months and the employer may dispense with the services of the worker during this period without warning and without end of service reward. The worker may not be appointed. Under experience more than once with one employer, and if the worker successfully passed the period of the experiment and continued to work, the period of service shall be calculated.