I wrote two functions and now I would love to find out, which of them is faster. How can I find it out, which one is faster?
How can I find out by testing, which one is faster? Do go provide a timer for that?
Even better, Go provides a built in benchmark and testing functionality!
Create a file named something_test.go (must have the _test part).
func BenchmarkFunc1(b *testing.B) {
for i := 0; i < b.N; i++ {
_ = Func1()
}
}
func BenchmarkFunc2(b *testing.B) {
for i := 0; i < b.N; i++ {
_ = Func2()
}
}
Then simply run: go test -bench=. -benchmem
It will print how long each function took and memory usage / allocations.
Ref:
http://golang.org/pkg/testing/
http://dave.cheney.net/2013/06/30/how-to-write-benchmarks-in-go
You could write a benchmark for each function.
See for instance "How to write benchmarks in Go"
// from source_test.go
func BenchmarkFunction1(b *testing.B) {
// run the Function1 function b.N times
for n := 0; n < b.N; n++ {
Function1(10)
}
}
Repeat for Function2 and check the results with go test -bench=.
Related
Disclaimer: I wish you a merry XMas and I hope my question does not disturb you!
sample.go:
package main
import(
"fmt"
"os"
)
type sample struct {
value int64
}
func (s sample) useful() {
if s.value == 0 {
fmt.Println("Error: something is wrong!")
os.Exit(1)
} else {
fmt.Println("May the force be with you!")
}
}
func main() {
s := sample{42}
s.useful()
s.value = 0
s.useful()
}
// output:
// May the force be with you!
// Error: something is wrong!
// exit status 1
I did a lot of research on how to use interfaces in golang testing. But so far I was not able to wrap my head around this completely. At least I can not see how interfaces help me when I need to "mock" (apologies for using this word) golang std. library packages like "fmt".
I came up with two scenarios:
use os/exec to test the command line interface
wrap fmt package so I have control and am able to check the output strings
I do not like both scenarios:
I experience going through the actual command line a convoluted and not-performant (see below). Might have portability issues, too.
I believe this is the way to go but I fear that wrapping the fmt package might be a lot of work (at least wrapping the time package for testing turned out a non-trivial task (https://github.com/finklabs/ttime)).
Actual Question here: Is there another (better/simpler/idiomatic) way?
Note: I want to do this in pure golang, I am not interested in the next testing framework.
cli_test.go:
package main
import(
"os/exec"
"testing"
)
func TestCli(t *testing.T) {
out, err := exec.Command("go run sample.go").Output()
if err != nil {
t.Fatal(err)
}
if string(out) != "May the force be with you!\nError: this is broken and not useful!\nexit status 1" {
t.Fatal("There is something wrong with the CLI")
}
}
Chapter 11 of Kerningham's Book gives a good solution to this question.
The trick is to change the calls to fmt.Printline() to calls to
fmt.Fprint(out, ...) where out is initialised to os.Stdout
This can be overwritten in the test harness to new(bytes.Buffer) allowing the
test to capture the output.
See https://github.com/adonovan/gopl.io/blob/master/ch11/echo/echo.go and
https://github.com/adonovan/gopl.io/blob/master/ch11/echo/echo_test.go
edited by OP...
sample.go:
package main
import(
"fmt"
"os"
"io"
)
var out io.Writer = os.Stdout // modified during testing
var exit func(code int) = os.Exit
type sample struct {
value int64
}
func (s sample) useful() {
if s.value == 0 {
fmt.Fprint(out, "Error: something is wrong!\n")
exit(1)
} else {
fmt.Fprint(out, "May the force be with you!\n")
}
}
func main() {
s := sample{42}
s.useful()
s.value = 0
s.useful()
}
// output:
// May the force be with you!
// Error: this is broken and not useful!
// exit status 1
cli_test.go:
package main
import(
"bytes"
"testing"
)
func TestUsefulPositive(t *testing.T) {
bak := out
out = new(bytes.Buffer)
defer func() { out = bak }()
s := sample{42}
s.useful()
if out.(*bytes.Buffer).String() != "May the force be with you!\n" {
t.Fatal("There is something wrong with the CLI")
}
}
func TestUsefulNegative(t *testing.T) {
bak := out
out = new(bytes.Buffer)
defer func() { out = bak }()
code := 0
osexit := exit
exit = func(c int) { code = c }
defer func() { exit = osexit }()
s := sample{0}
s.useful()
if out.(*bytes.Buffer).String() != "Error: something is wrong!\n" {
t.Fatal("There is something wrong with the CLI")
}
if code != 1 {
t.Fatal("Wrong exit code!")
}
}
Am I missing something here or are you talking of testable examples?
Basically, it works like this: In a *_test.go file, you need to adhere to the convention Example[[T][_M]] where T is a placeholder for the type and M a placeholder for the method you want to display the testable example as example code in the Godoc. If the function is just called Example(), the code will be shown as a package example.
Below the last line of the code of your example, you can put a comment like this
// Output:
// Foo
Now go test will make sure that the testable example function either exactly puts out everything below // Output: (including whitespace) or it will make the test fail.
Here is an actual example for an testable example
func ExampleMongoStore_Get() {
sessionId := "ExampleGetSession"
data, err := ms.Get(sessionId)
if err == sessionmw.ErrSessionNotFound {
fmt.Printf("Session '%s' not found\n", sessionId)
data = make(map[string]interface{})
data["foo"] = "bar"
ms.Save(sessionId, data)
}
loaded, _ := ms.Get(sessionId)
fmt.Printf("Loaded value '%s' for key '%s' in session '%s'",
loaded["foo"],
"foo", sessionId)
// Output:
// Session 'ExampleGetSession' not found
// Loaded value 'bar' for key 'foo' in session 'ExampleGetSession'
}
Edit: Have a look at the output of above example at godoc.org
I'm learning Rust, so I'm doing the Project Euler problems, as they are good exercises imho.
But I'm already stuck on the second problem. The idea is to find the sum of all the even numbers that are less than 4000000 in the Fibonacci sequence.
So I tried to do it a bit the functional way, and using a custom iterator :
use std::mem;
static LIMIT: uint = 4000000u;
struct Fibonacci {
current: uint,
next: uint,
limit: uint,
}
fn fibo(lim: uint) -> Fibonacci {
Fibonacci {
current: 1u, next: 1u, limit: lim
}
}
impl Iterator<uint> for Fibonacci {
fn next(&mut self) -> Option<uint> {
let nex = self.current + self.next;
let cur = mem::replace(&mut self.next, nex);
if cur >= self.limit { return None; }
Some(mem::replace(&mut self.current, cur))
}
}
fn main() {
let sum = fibo(LIMIT).filter(|&x| x%2 == 0).fold(0, |sum, x| sum + x);
println!("Sum of fibs : {}", sum);
}
It looks good, and it gives the correct Fibonacci sequence (I verified with println!s).
The problem is that it doesn't give the correct sum : it outputs 1089154 whereas it should output 4613732. To me it seems that the fold misses the last number, but I can't see why !
I'm a total beginner with Rust, so any help would be greatly appreciated, thanks !
What you should be testing in your exit branch is the value of self.current; instead, you're testing the value of self.next. In other words, you're failing to output the last number in the sequence (as Matthieu suggested).
I verified that if the iterator is implemented correctly, it should produce the correct result with this (using grabbag_macros = "0.0.1" as a Cargo dependency):
#![feature(phase)]
#[phase(plugin, link)] extern crate grabbag_macros;
static LIMIT: u64 = 4000000;
fn main() {
let sum = recurrence![f[n]: u64 = 1, 1... f[n-1] + f[n-2]]
.take_while(|&n| n <= LIMIT)
.filter(|&n| n % 2 == 0)
.fold(0, |a, b| a + b);
println!("Sum of fibs: {}", sum);
}
A few other random notes: I'd avoid uint for this, since it's platform-dependent. You don't need the u suffix unless you need to be specific about the type. You can use take_while or plain old take instead of hard-coding a limit into your iterator.
I have a simple function I want to test:
func (t *Thing) print(min_verbosity int, message string) {
if t.verbosity >= minv {
fmt.Print(message)
}
}
But how can I test what the function actually sends to standard output? Test::Output does what I want in Perl. I know I could write all my own boilerplate to do the same in Go (as described here):
orig = os.Stdout
r,w,_ = os.Pipe()
thing.print("Some message")
var buf bytes.Buffer
io.Copy(&buf, r)
w.Close()
os.Stdout = orig
if(buf.String() != "Some message") {
t.Error("Failure!")
}
But that's a lot of extra work for every single test. I'm hoping there's a more standard way, or perhaps an abstraction library to handle this.
One thing to also remember, there's nothing stopping you from writing functions to avoid the boilerplate.
For example I have a command line app that uses log and I wrote this function:
func captureOutput(f func()) string {
var buf bytes.Buffer
log.SetOutput(&buf)
f()
log.SetOutput(os.Stderr)
return buf.String()
}
Then used it like this:
output := captureOutput(func() {
client.RemoveCertificate("www.example.com")
})
assert.Equal(t, "removed certificate www.example.com\n", output)
Using this assert library: http://godoc.org/github.com/stretchr/testify/assert.
You can do one of three things. The first is to use Examples.
The package also runs and verifies example code. Example functions may include a concluding line comment that begins with "Output:" and is compared with the standard output of the function when the tests are run. (The comparison ignores leading and trailing space.) These are examples of an example:
func ExampleHello() {
fmt.Println("hello")
// Output: hello
}
The second (and more appropriate, IMO) is to use fake functions for your IO. In your code you do:
var myPrint = fmt.Print
func (t *Thing) print(min_verbosity int, message string) {
if t.verbosity >= minv {
myPrint(message) // N.B.
}
}
And in your tests:
func init() {
myPrint = fakePrint // fakePrint records everything it's supposed to print.
}
func Test...
The third is to use fmt.Fprintf with an io.Writer that is os.Stdout in production code, but bytes.Buffer in tests.
You could consider adding a return statement to your function to return the string that is actually printed out.
func (t *Thing) print(min_verbosity int, message string) string {
if t.verbosity >= minv {
fmt.Print(message)
return message
}
return ""
}
Now, your test could just check the returned string against an expected string (rather than the print out). Maybe a bit more in-line with Test Driven Development (TDD).
And, in your production code, nothing would need to change, since you don't have to assign the return value of a function if you don't need it.
I was wondering if it is possible to dynamically create variables in Go?
I have provided a pseudo-code below to illustrate what I mean. I am storing the newly created variables in a slice:
func method() {
slice := make([]type)
for(i=0;i<10;i++)
{
var variable+i=i;
slice := append(slice, variablei)
}
}
At the end of the loop, the slice should contain the variables: variable1, variable2...variable9
Go has no dynamic variables.
Dynamic variables in most languages are implemented as Map (Hashtable).
So you can have one of following maps in your code that will do what you want
var m1 map[string]int
var m2 map[string]string
var m3 map[string]interface{}
here is Go code that does what you what
http://play.golang.org/p/d4aKTi1OB0
package main
import "fmt"
func method() []int {
var slice []int
for i := 0; i < 10; i++ {
m1 := map[string]int{}
key := fmt.Sprintf("variable%d", i)
m1[key] = i
slice = append(slice, m1[key])
}
return slice
}
func main() {
fmt.Println(method())
}
No; you cannot refer to local variables if you don’t know their names at compile-time.
If you need the extra indirection you can do it using pointers instead.
func function() {
slice := []*int{}
for i := 0; i < 10; i++ {
variable := i
slice = append(slice, &variable)
}
// slice now contains ten pointers to integers
}
Also note that the parentheses in the for loop ought to be omitted, and putting the opening brace on a new line is a syntax error due to automatic semicolon insertion after ++. makeing a slice requires you to pass a length, hence I don’t use it since append is used anyway.
I brute-forced summing of all primes under 2000000. After that, just for fun I tried to parallel my for, but I was a little bit surprised when I saw that Parallel.For gives me an incorrect sum!
Here's my code : (C#)
static class Problem
{
public static long Solution()
{
long sum = 0;
//Correct result is 142913828922
//Parallel.For(2, 2000000, i =>
// {
// if (IsPrime(i)) sum += i;
// });
for (int i = 2; i < 2000000; i++)
{
if (IsPrime(i)) sum += i;
}
return sum;
}
private static bool IsPrime(int value)
{
for (int i = 2; i <= (int)Math.Sqrt(value); i++)
{
if (value % i == 0) return false;
}
return true;
}
}
I know that brute-force is pretty bad solution here but that is not a question about that. I think I've made some very stupid mistake, but I just can't locate it. So, for is calculating correctly, but Parallel.For is not.
You are accessing the variable sum from multiple threads without locking it, so it is possible that the read / write operations become overlapped.
Adding a lock will correct the result (but you will be effectively serializing the computation, losing the benefit you were aiming for).
You should instead calculate a subtotal on each thread and add the sub-totals at the end. See the article How to: Write a Parallel.For Loop That Has Thread-Local Variables on MSDN for more details.
long total = 0;
// Use type parameter to make subtotal a long, not an int
Parallel.For<long>(0, nums.Length, () => 0, (j, loop, subtotal) =>
{
subtotal += nums[j];
return subtotal;
},
(x) => Interlocked.Add(ref total, x)
);
Many thanks to all of you for your quick answers
i changed
sum += i;
to
Interlocked.Add(ref sum,i);
and now it works great.