To test small snippets of Go code you can use one of several on-line playgrounds.

Go Playground

The Go Playground or slightly nicer The Go Play Space.

Playground has some limitations:

• only supports the standard library; you can’t use third party libraries
• networking, file i/o is not available
• time is fixed

Playground gives you a permanent link to code snippet for sharing with others.

Glot

Glot.io can execute code in multiple languages, including Go.

Its limitations are:

• only supports the standard library, you can't use third party libraries
• networking is not available
• doesn't have a way to format code

You can create shareable snippets.

Repl.it

Repl.it can execute code in multiple languages, including Go.

Its limitations are:

• only supports the standard library, you can't use third party libraries