You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: atomic_credentials_test.go
    path of file: ./repos/flyte/flyteidl/clients/go/admin
    
    the code of the file until where you have to start completion: package admin

import (
	"context"
	"fmt"
	
    
func ExampleNewPerRPCCredentialsFuture() {
	f := NewPerRPCCredentialsFuture()

	// Starts uninitialized
	fmt.Println("Initialized:", f.IsInitialized())

	// Implements credentials.PerRPCCredentials so can be used as one
	m, err := f.GetRequestMetadata(context.TODO(), "")
	fmt.Println("GetRequestMetadata:", m, "Error:", err)

	// Materialize the value later and populate
	tokenSource := DummyTestTokenSource{}
	f.Store(NewCustomHeaderTokenSource(tokenSource, false, "my_custom_header"))

	// Future calls to credentials.PerRPCCredentials methods will use the new instance
	m, err = f.GetRequestMetadata(context.TODO(), "")
	fmt.Println("GetRequestMetadata:", m, "Error:", err)

	// Output:
	// Initialized: false
	// GetRequestMetadata: map[] Error: <nil>
	// GetRequestMetadata: map[my_custom_header:Bearer abc] Error: <nil>
}