Instruction: Generate an answer to the question by utilizing the information contained in the document.

Input:
Question: How do you test if the S-40M is good?  I think mine is defective.
Document: Mine arrived with the red test button broken. I emailed Cowboy Studio and they shipped a new one to me right away. The flash works as planned. It flashes whenever it detects another flash going off.
A very nice little in size but yet powerful 40W-S light. You can use it for many imaginative purposes (as noted here and in other reviews), such as those in the subject line.The sensitive built-in triggering works well to trigger the flash in most but not all cases, I don't consider this a drawback, but something to test when setting up. It's a real nice feature to have on the head.
This product was defective when I received it. I found it to be flimsy at best. I returned the product.
I have noticed most of the bad reviews on here involve faulty units. A shame but I wonder if some of that might be from the shipping? Mine came in just recently and works fine. Nice price if you are just learning.
I do not wait nothing fancy but waiting for working product.I am wrong ,test button is not working,power indicator is not working and ready lights is not working.I have too expansive mini tripoid now ;(.Slave is some times working.I do not buy this product again.
I have a light meter but I have found it is just as quick to guess the exposure and take some test shots. There is a hole/screw to insert and secure an umbrella but the stand base is too small to support an umbrella without tipping over. You can fix this by either weighing down the legs or using a larger stand.
Upon receipt of the product, tried to screw the light into the socket and it went in with much difficulty. When unscrewing it, the metal threading pulled out of the plastic base. I thought it was one that might be defective so I ordered another to replace it. That one did the same thing. Returned all I ordered and will not recommend these to anyone.
I need a backup Strobe Flash Light, and this are AWESOME!! !I have a Elinchrom D-Lite 4 Studio Flash Light, and sometimes i need a backlight or a lightweight strobe flash light to work outside. I buy to kits of this Cowboystudio (for test) and there are great!. The light is very powerful, great to use as backlight.
I must say I was skeptical if this was worth it, but since I was wanting to test out using slaves/strobes versus continuous lighting, I decided for the price I might as well just buy it. I have used it for one session so far, with my continuous lighting and this was used for a background filler. It worked GREAT with the on camera flash!
Amazon sells this for about $45. I got mine at bhphotovideo for $30.2) Assemble the strobe unit. This part is self-explanatory. No moredifficult than setting up a tripod, really. There are some instructions atthe cowboy studio web page for this part.3) Once assembled take a look at the head of the unit. I'm calling it the head but there may be another name that I'm unaware of. I'm referring to the part that holds the flash bulb.
Answer: The light was defective when's tarried.  I returned it.  I did not get another one.