Go: Getting Started - Hello World

Following the Learn Go with Tests guide, starting with a Hello World example that demonstrates Go’s syntax, testing approach, and basic development workflow.

Getting Started with Go

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Go is a programming language developed by Google. Tests are written using the built-in testing package without requiring external frameworks.

Setting Up the Project

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First, let’s create a simple Go module go mod init <modulepath>. In Go, every project starts with a go.mod file:

module example.com/hello

go 1.25.5

This creates a module named example.com/hello using Go version 1.25.5. The module name doesn’t need to be a real URL for local projects.

Hello World

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Simple hello.go file that demonstrates Go’s basic syntax and features:

package main

import "fmt"

const spanish = "Spanish"
const french = "French"

const spanishHelloPrefix = "Hola, "
const englishHelloPrefix = "Hello, "
const frenchHelloPrefix = "Bonjour, "

func Hello(name string, language string) string {
	if name == "" {
		name = "World"
	}

	prefix := greetingsPrefix(language)

	return prefix + name
}

func greetingsPrefix(language string) (prefix string) {
	switch language {
	case spanish:
		prefix = spanishHelloPrefix
	case french:
		prefix = frenchHelloPrefix
	default:
		prefix = englishHelloPrefix
	}
	return
}

func main() {
	fmt.Println(Hello("Roman", ""))
}

Package Declaration: Every Go file starts with a package declaration. The main package is special, it creates an executable program.

Constants: Go uses const for immutable values.

Functions: Go functions are declared with func. The return type comes after the parameter list: func Hello(name string, language string) string

Named Return Values: In greetingsPrefix, we use a named return value (prefix string). This creates a variable called prefix that we can modify and return implicitly with just return.

Hello World Tests

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Go includes a testing package in the standard library. Test files end with _test.go:

package main

import "testing"

func TestHello(t *testing.T) {
	t.Run("saying hello to people", func(t *testing.T) {
		got := Hello("Roman", "")
		want := "Hello, Roman"

		assertCorrectMessage(t, got, want)
	})
	t.Run("say 'Hello, World' when an empty string is supplied", func(t *testing.T) {
		got := Hello("", "")
		want := "Hello, World"

		assertCorrectMessage(t, got, want)
	})
	t.Run("in spanish", func(t *testing.T) {
		got := Hello("Elodie", "Spanish")
		want := "Hola, Elodie"

		assertCorrectMessage(t, got, want)
	})
	t.Run("in french", func(t *testing.T) {
		got := Hello("Elodie", "French")
		want := "Bonjour, Elodie"

		assertCorrectMessage(t, got, want)
	})
}

func assertCorrectMessage(t testing.TB, got, want string) {
	t.Helper()
	if got != want {
		t.Errorf("got %q want %q", got, want)
	}
}

Test Functions: Test functions must start with Test and take a *testing.T parameter.

Subtests: t.Run() creates subtests to organize related test cases and show which specific case failed.

Helper Functions: The assertCorrectMessage function uses t.Helper() to mark itself as a test helper. When tests fail, the error points to the calling test rather than the helper function.

Error Reporting: t.Errorf() reports test failures with formatted output. The %q verb adds quotes around strings to show whitespace differences.

Running Tests

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go test ./...        # Run all tests in current directory and subdirectories
go test -v           # Run tests with verbose output
go test -cover       # Run tests and show coverage
go test -run TestHello  # Run specific test function

Development Tools

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# Documentation
go doc fmt

# Local documentation server
go install golang.org/x/pkgsite/cmd/pkgsite@latest
pkgsite -open .

# Test runner
go install gotest.tools/gotestsum@latest