How do I properly unit test a post request?

    public interface IFacilityService
    {
        Task<Facility> CreateFacilityAsync(Facility facility);
    }

    public interface IFacilityService
    {
        Task<Facility> CreateFacilityAsync(Facility facility);
    }

        public async Task<Facility> CreateFacilityAsync(Facility facility)
        {
            _db.Facilities.Add(facility);
            await _db.SaveChangesAsync();
            return facility;
        }

        public async Task<Facility> CreateFacilityAsync(Facility facility)
        {
            _db.Facilities.Add(facility);
            await _db.SaveChangesAsync();
            return facility;
        }

        [HttpPost("facility")]
        public async Task<IActionResult> CreateFacilityAsync([FromBody] Facility facilityRequest)
        {
            var createdFacility = await _facilityService.CreateFacilityAsync(facilityRequest);
            return Ok(createdFacility);
        }

        [HttpPost("facility")]
        public async Task<IActionResult> CreateFacilityAsync([FromBody] Facility facilityRequest)
        {
            var createdFacility = await _facilityService.CreateFacilityAsync(facilityRequest);
            return Ok(createdFacility);
        }