Capturing stdout or fmt.Println outputs during Testing

My main file example.go has a simple fmt.Println statement, how do I capture during testing. Below is an example:

example.go

package main

import "fmt"

func main() {
    fmt.Printf("testing")
    a := 1
    fmt.Printf(": %d", a)
}

example_test.go

package main

func Testmain(t *testing.T) {
    // mainOutput := ?
    if mainOutput != "testing: 1" {
        t.Error("Output is not what expected!!!")
    }
}

How I can capture main's fmt.Println Output to validate it. What should I replace // mainOutput := ? to capture the output. Any inputs.