You can contact and check their references if they have any. If they don't have any references, don't hire them.

Something like Codility perhaps?

Edit: keep in mind that this sort of tests tell you how well a person is versed into language syntax and algorithms but don't tell you the whole picture i.e. if the person is actually a good developer or not. A developer might know all of a language's syntax etc and be very good at algorithms and still produce sub par software. I say this as one who has had to hire several developers over the past several years.

Trying to figure out if someone can code is pretty much useless. Anyone can google, copy, paste, and call it good. Instead, ask them how they would solve a problem you have, what language they would use, what sort of functions they would create to do it. Then have them produce a small example and run it using Google Developer Tools, look into the profile of it and see what kind of timing issues they create, if there are any issues, etc. It's not fool proof, but it's important to know how they think and what they are capable of on the spot.

What i do when i hire someone for my company is to give them a technical test and then have a call with them where they explain everything they did in the test. Also i asked them a lot of other questions during the call so i can hear their answers live without them having time to search on Google for an answer.

There are some online tools available online to measure the skills of a developer that includes programming or coding tests and aptitude tests. Some that I can suggest that are used by large companies are Codility, TestDome, and Mettl. I think it is great to use the tools as a reference but it should still depend on your judgement if the developer is reliable and can be trusted with a project.

If I am on your situation with limited knowledge on programming or coding, I will assess the developer's knowledge by giving the developer some test projects and see how efficient he can do it. Time is important since you will see there how well he knows what he does best. Also, another thing to consider is his past projects. Ask for a portfolio, some websites that he developed, or published software or application. Always ask relevant questions, maybe try to ask misleading ones as well as if a person really knows the topic at hand he will definitely correct you.

I agree with the previous posts. In addition to that, contact his cited references. If the developer only provided a website, try to contact the site owner to get more insight on how he is as an employee. Give a small project idea and ask the developer to what is the best programming language he will use specifically for that. I am not sure with online tests since not all developers are familiar with different platforms, most stick to one language and has familiarity with related languages associated to the main one they mostly use.

As a programmer... there are many ways that people can write code (good or bad) to achieve a given result.

If you are not a coder yourself it is pretty difficult but here some tips.

- Assign them a small project to assess them (time wise and quality wise): you will be able to test their communication skills, the capacity to understand your instructions and to transform it into "code".

- Read the code through: is the code well commented? Do all functions are well commented specifying what parameters are required and why?

- Are all the variables "making sense" with names like "numberOfDownloads" (with this strange style called "camel case") instead of using something like "nd2" without you or any third party going to be nuts to understand?

Hi,
It's good to check your skills that will let you know the level of your knowledge. This will test your programming level standard.
Yes, there is a way to check your developers' coding skills. Here is a platform through which you can verify the programming skills of a candidate. Tests4Geeks provides you the coding quiz to test the knowledge easily.
We offer 2 free tests and then you can buy discounted multi month packages for companies.

You can contact them directly and ask them to show you the references

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It's tough to know if a developer is good or not if you're not a developer yourself.