Saravanan Gnanaguru

Posted on Jul 13, 2020 • Updated on Jan 12, 2021

Go Hello World! Program

#go #beginners #tutorial

Table of Content

Introduction
Go Development Space
Go Program Structure
Writing Go Unit Test
Key Take Away

Introduction

As part of Go Tutorial series, we have gone through the steps to install and setup Go development environment in my previous article.

In this blog, let us get started to write a Hello World! program in Go.

Go Development Space

After installing platform specific go installer. We need to setup $GOPATH environment variable. Refer the Go Getting Started blog
Go programs should be written inside the $GOPATH/src directory.
Execute the below commands, to get started with Hello World! Go program development

cd $GOPATH/src
mkdir helloworld
cd helloworld

vim main.go

Go Program Structure

Let us start writing the main.go file.

Package

Every go program starts with a package declaration. package is nothing but the modules for doing specific operation.
package statement should be first executable line in Go program.

package main

package main is the entry point module for Go programs. We can have as many number of packages in our project. But main package is the beginning for Go program execution.

Import statement

Import statement block should contain the modules used in the program.
We will be using the Go module fmt, to print the Hello World! string to the console.
Below is the import code snippet

import (
  "fmt"
)

Function main

Since go is inspired from C++ and Java, we need to declare main() function in Go as well.
This function calls the rest of other methods and functions

func main() {
  val := print()
  fmt.Println(val)
}

Function print

Finally we will code the print function, to display the text in console output.
This function has been invoked in the func main()

func print() string {
  str := "Hello World!"
  return str
}

Full source code

The main.go looks like the below

// Go Program to print the string "Hello World!"
package main

import (
  "fmt"
)

func main() {
  val := print()
  fmt.Println(val)
}

func print() string {
  str := "Hello World!"
  return str
}

Build and Run

Initialize the module file

Run the command below to initialize the module and prepare to execute

go mod init

Build code and Run executable

Run the command below to build the code

go build main.go -o helloworld

This command generates an executable file helloworld in the current directory.
Execute the executable helloworld. It print the value,

Hello World!

Alternate Execute Method

Instead building and running the executable. We can also directly execute the go source file using go run command,
Execute the command after doing go mod init

go run hiworld.go

Writing Go Unit Test

Go provides the built-in functionality to test your Go code. Hence, we don't need an expensive setup or 3rd party libraries to create unit tests.
Go has the module called testing to achieve the same.
So if we want to test a go program, we can create a unit test file with <source_go_filename>_test.go.
For example: We have created main.go source file. So create test file as main_test.go to unit test the main.go functionality.

Go Unit Test Program Structure.

Go test program also follows the similar statement pattern as main source go file.
It should have the below sections,
- package statement
- import statement
- func main()

Go Unit Test Program

Below is the unit test main_test.go code for our main.go source file,

package main

import "testing"

func TestHello(t *testing.T) {
    expected := "Hello World!"
    if got := print(); got != expected {
        t.Errorf("print() = %q, want %q", got, expected)
    }
}

Execute the Unit Test

Run the below command to execute the Unit test for main.go

go test

This command expects the _test.go file and runs the test cases coded in main_test.go file.
The test run outputs the below in console, if the test is passed.

PASS
ok      main 0.002s

Key Take-Away

We have covered the topics below in this blog,
- Go development basics
- Develop Go program
- Go program build and execute methods
- Creating Go unit test methods

Hope the blog content is useful.

Bibliography

Go By Example-HelloWorld
Go unit testing

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