learn-golang-with-tdd

Notes about the things I learnt while reading/practicing with Learn Go with Tests.

[TOC]

Hello, World

• https://quii.gitbook.io/learn-go-with-tests/go-fundamentals/hello-world

What I learned

• if works like other programming languages, without (parenthesis)
• blocks are defined with {curly braces}
• variables are assigned declared like this: varName := value
  • I researched and realized that
    • := for short variable declarations
    • = for variable declarations and assignments.
• t.Errorf prints a message when a test fails.
• %q means "string surrounded with double quotes", in the string format context
• func greetingPrefix(language string) (prefix string) creates a named return value
  - this creates a variable called prefix in the function
  - it will be assigned the "zero" value. In this case (string): ""
• in Go, public functions start with a capital letter and private ones start with a lowercase.

Few rules to writing tests

• file name must be ${something}_test.go
• the test function must start with Test
• test function takes only one argument t *testing.T
• in order to use *testing.T type you need to import "testing"

godoc and the PATH

# installing local documentation
go install golang.org/x/tools/cmd/godoc@latest

# after installing the godoc command isn't available
# in the path! I had to call it via:
~/.asdf/installs/golang/1.21.7/packages/bin/godoc -http :8000

Starting a module

create the hello module:

mkdir hello
cd hello
go mod init hello
# check if the "go.mod" file was created

hello.go:

package main

import "fmt"

// Hello() is a separated function
// to make it testable
func Hello() string {
  return "Hello, world"
}

func main() {
  fmt.Println(Hello())
}

hello_test.go:

package main

import "testing"

func TestHello(t *testing.T) {
  got := Hello()
  want := "Hello, world"

  if got != want {
    t.Errorf("got %q want %q", got, want)
  }
}

Run the test:

go test

integers

• https://quii.gitbook.io/learn-go-with-tests/go-fundamentals/integers

Testable Examples

official docs

• resides in the _test.go file
• starts with Example
• the // Output: part is mandatory
• run go test -v to see it being executed

func ExampleAdd() {
	sum := Add(1, 5)
	fmt.Println(sum)
	// Output: 6
}

iterations

• https://quii.gitbook.io/learn-go-with-tests/go-fundamentals/iteration

for loops

• for is the only way to loop in Golang
• it can be used in some different ways: examples of for

benchmarking

• official docs

This goes in the repeat_test.go file:

func BenchmarkRepeat(b *testing.B) {
  for i := 0; i < b.N; i++ {
    Repeat("a")
  }
}

The code is very similar to a test.

The testing.B gives you access to the cryptically named b.N.

When the benchmark code is executed, it runs b.N times and measures how long it takes.

The amount of times the code is run shouldn't matter to you, the framework will determine what is a "good" value for that to let you have some decent results.

To run the benchmarks do go test -bench=.

$ go test -bench=.
goos: darwin
goarch: arm64
pkg: iteration
BenchmarkRepeat-8       15226100                79.48 ns/op
PASS
ok      iteration       2.719s

The test was executed 15,226,100 times. Each execution took on average 79.42 nanoseconds to run.