How can I do test setup using the testing package in Go

This can be achieved by putting a init() function in the myfile_test.go file. This will be run before the init() function.

// myfile_test.go
package main

func init() {
     /* load test data */
}

The myfile_test.init() will be called before the package init() function.

Starting with Go 1.4 you can implement setup/teardown (no need to copy your functions before/after each test). The documentation is outlined here in the Main section:

TestMain runs in the main goroutine and can do whatever setup and teardown is necessary around a call to m.Run. It should then call os.Exit with the result of m.Run

It took me some time to figure out that this means that if a test contains a function func TestMain(m *testing.M) then this function will be called instead of running the test. And in this function I can define how the tests will run. For example I can implement global setup and teardown:

func TestMain(m *testing.M) {
    setup()
    code := m.Run() 
    shutdown()
    os.Exit(code)
}

A couple of other examples can be found here.

The TestMain feature added to Go’s testing framework in the latest release is a simple solution for several testing use cases. TestMain provides a global hook to perform setup and shutdown, control the testing environment, run different code in a child process, or check for resources leaked by test code. Most packages will not need a TestMain, but it is a welcome addition for those times when it is needed.