This really depends on the idea that you want to test. Remember, a test is just a test, and not a complete depiction of how your actual business will do once it launches as that greatly depends not only on your product, but also on how your business is managed and what value you provide to the customers.

Having said that, a good test can give you good validation on your product/service. If it's a product, you can use crowdfunding or Quirky to test the interest. If it's a service, you can create a signup page, and raise awareness it via well thought out plan that includes blogs, partners, paid advertising and other marketing channels. In addition, there is no substitute to talk to people in person (offline). It will help you describe your idea in detail to a potential customer, and gauge their true reaction w/ verbal feedback as well as facial expressions, body language etc.

Sweet Question!!
There is no 1 approach, the idea though to get feedback.
Depending on the idea and your entrepreneurial spirit (or lack of), you can visit Quirky.com where a community votes and then helps you create the idea and retail it.
During startup weekend events entrepreneurs are asked to hit the streets with surveys or mock ups and get people's reactions and emails or orders, etc.
You can create Facebook page with samples and prototypes and get followers feedback and acceptance.
Of course you have Kickstarter or indiegogo and even gofundme.

If you idea is programming intensive you are better learning it than trying to find a coder who will love your idea and join with no pay. They are in super high demand. A class I took for swift for example helped me a lot. Here is the site http://mbsy.co/c6bPT
For my first ever startup it took me a year to find my first programming partner. We eventually made a good return... But the thing though is that we cut it close because others were developing the same marketing software. In entrepreneurship saved time is key.
They make learning super easy.

There are ways in which not only can you validate but have the community find your venture. Learn to code if needed, design a sample and show it in a video to them and ask for support. :) good luck.

On a small scale your ability to sell the value of your idea ultimately must be validated by someone’s willingness to pay you. That is the first thing to work on, does your idea cause people to pull out their wallets and pay for the product?

But what if the product/service doesn't exist yet?

When you are going through the process of validating if an idea works you must create some type of prototype. This does not need to be the finished product or even something that is tangible. For example you can act as if the service/product already exist and create a website around it. On the website you can inform people to submit their email to be notified about the product/service.

Many email subscribers is an indicator that there is interest and you are building an audience to market to in the future.

Also asks yourself these questions:
What problem does this idea solve?
Who is my ideal customer?
Who are my competitors?
Is my idea scalable?
What are the benefits of the idea? (How does this make people better?)
What are the features of the product/service?

Here is a really good example of how a startup validated their product without building it.

The startup is called SendWithUS.

They wanted to:
a) gauge interest in a transactional email service, and
b) measure what features mattered the most to customers.

To accomplish this they decided to build a website that seemingly offered many features and measured which ones customers were most interested in. Once they had an answer, they’d build an MVP focusing on those features. Easy, Smart and Lean :)

See the full case study here: http://goo.gl/k1UOGP

Hope this helps.
Good luck building your MVP and the startup!
Alex Shakaryan

PS. Let me know if you need assistance on applying this method to your idea.