I want to create a database driven application using Golang. I am trying to do it TDD way.
When I try to test methods that make Sql queries, What all are the packages available ?
I don't want to connect to the default database that I use for development. I can write code to take up another test database while running a test, but is there any go library that already does it.
Is there any library that does db tests without connecting to database at all ?
What is the standard way to do database test with golang ?
I had a similar question not long ago when refactoring some of my own tests, and there's a couple of ways you can do it:
a) Provide an exported type and an Open or Connect function that returns it - e.g.
type DB struct {
db *sql.DB
}
// Using http://jmoiron.github.io/sqlx/ for this example, but
// it has the same interface as database/sql
func Open(opts *Options) (*DB, error) {
db, err := sqlx.Connect(opts.Driver, fmt.Sprintf("host=%s user=%s dbname=%s sslmode=%s", opts.Host, opts.User, opts.Name, opts.SSL))
if err != nil {
return nil, err
}
return &DB{db}, nil
}
... and then each of your tests, write setup & teardown functions that return an instance of *DB that you define your database functions on (as methods - i.e. func (db *DB) GetUser(user *User) (bool, error)):
// Setup the test environment.
func setup() (*DB, error) {
err := withTestDB()
if err != nil {
return nil, err
}
// testOptions is a global in this case, but you could easily
// create one per-test
db, err := Open(testOptions)
if err != nil {
return nil, err
}
// Loads our test schema
db.MustLoad()
return db, nil
}
// Create our test database.
func withTestDB() error {
db, err := open()
if err != nil {
return err
}
defer db.Close()
_, err = db.Exec(fmt.Sprintf("CREATE DATABASE %s;", testOptions.Name))
if err != nil {
return err
}
return nil
}
Note that this is somewhat "integration" testing, but I strongly prefer to test against a "real" database since mocking the interface won't help you catch issues with your queries/query syntax.
b) The alternative, although less extensible on the application side, is to have a global db *sql.DB variable that you initialise in init() within your tests—since tests have no guaranteed order you'll need to use init()—and then run your tests from there. i.e.
var db *sql.DB
func init() {
var err error
// Note the = and *not* the assignment - we don't want to shadow our global
db, err = sqlx.Connect(...)
if err != nil {
...
}
err := db.loadTestSchema
// etc.
}
func TestGetUser(t *testing.T) {
user := User{}
exists, err := db.GetUser(user)
...
}
You can find some practical examples in drone.io's GitHub repo, and I'd also recommend this article on structuring Go applications (especially the DB stuff).
I use a global variable to store the data source (or connection string) of current database and set to different value in test function. Since there is only one database I need to operate so I choose the easiest way.
I am learning how to create Golang tests for an Appengine app.
The documentation examples don't make sense to me.
https://cloud.google.com/appengine/docs/standard/go/tools/localunittesting/reference
Documentation seems to say you can create a context := aetest.NewContext()
When I attempt to do so, I'm getting an error that aetest.NewContext requires arguments.
$ go test -v
./skincare_test.go:12: not enough arguments in call to aetest.NewContext
have ()
want (*aetest.Options)
./skincare_test.go:12: assignment count mismatch: 3 = 2
FAIL _/Users/Bryan/work/gocode/skincarereview [build failed]
content of skincare_test.go:
package skincare
import (
"net/http"
"net/http/httptest"
"testing"
"appengine/aetest"
)
func TestIndexHandler(t *testing.T) {
ctx, done, err := aetest.NewContext()
if err != nil {
t.Fatal(err)
}
defer done()
req, err := http.NewRequest("GET", "/", nil)
if err != nil {
t.Fatal(err)
}
rr := httptest.NewRecorder()
handler := http.HandlerFunc(root)
handler.ServeHTTP(rr, req)
if status := rr.Code; status != http.StatusOK {
t.Errorf("handler returned wrong status code: got %v want %v",
status, http.StatusOK)
}
expected := "<div>Name"
if rr.Body.String() != expected {
t.Errorf("handler returned expected body: got %v want %v",
rr.Body.String(), expected)
}
}
I learn best by looking at example code, where can I find examples of Tests for Go web applications that use Appengine datastore?
The examples in the documentation are so simple that I don't see how I'm supposed to do more complicated testing.
It says 2 things:
1) You are missing a required parameter *aetest.Options
2) that you can NOT assign result aetest.NewContext() that consist of 2 variable to a set of 3 variables.
Check what is the output of the function. I guess it is just (context.Context, error) - I suspect the done is moved to the *aetest.Options somehow.
Unfortunately my access to docs is blocked right now.
You are using the old version of the app engine package (appengine/aetest instead of google.golang.org/appengine/aetest). The newer version does not require arguments.
Sorry for a bit dummy questions, but I'm kinda stuck.
So, I'm implementing wrapper above database driver for my application, and I need to keep it as portable as possible.
I came to decision that interfaces are perfect match for this task. So, I have my database struct with some variables and app-specific methods, and two interface functions:
query(request string) error
flush() int? string?? struct?? slice????, error
Now you probably got the main question. How do I do return data that type "flush()" doesn't know? Can I return it by interface, and if I can, how to work with that?
Second question is pretty basic, but still it isn't clear to me.
So, I have this database struct with two methods designed to be implemented by package user to use db driver he want.
Ho do I write it and how future implementation will look (there is an example on tour of go, but it's about interface for different structs with similar methods)
Hope you'll help me find an understanding :)
Yes, flush can just have the signiture;
flush() interface{}, error
How do you implement? Something like this with reasonable method bodies should do it for you;
type MyDbDriver struct {
//fields
}
func (d *MyDbDriver) query(request string) error {
return nil
}
func (d *MyDbDriver) flush() interface{}, error {
return nil, nil
}
In Go all interface implementations are implicit, meaning, if your type has methods that match the interfaces signature, then you've implemented it. No need for something like public class MyType: IMyInterface, IThisIsntCSharp. Note that in the example above *MyDbDriver has implemented your interface but MyDbDriver has not.
Edit: below a some pseudo calling code;
e := driver.query("select * from thatTable where ThatProperty = 'ThatValue'")
if e != nil {
return nil, e
}
i, err := driver.flush()
if err != nil {
return nil, err
}
MyConcreteInstance := i.(MyConcreteType)
// note that this will panic if the type of i is not MyConcreteType
// that can be avoided with the familiar object, err calling syntax
MyConcreteIntance, ok := i.(MyConcreteType)
if !ok {
// the type of i was not MyConcreteType :\
}
Is there a Go analogue to Python/Java's async datastore APIs? Or can one just use the normal API with the go keyword?
There is no Go equivalent to the Python or Java asynchronous APIs for any AppEngine service. In fact, the Go standard library has nothing in the standard asynchronous style either. The reason is that in Go, you write functions using a blocking style and compose them using some basic concurrency primitives based on need. While you cannot just tack go at the beginning of a dastore.Get call, it is still relatively straightforward. Consider the following, contrived example:
func loadUser(ctx appengine.Context, name strings) (*User, err) {
var u User
var entries []*Entry
done := make(chan error)
go func() {
// Load the main features of the User
key := datastore.NewKey(ctx, "user", name, 0, nil)
done <- datastore.Get(ctx, key)
}()
go func() {
// Load the entries associated with the user
q := datastore.NewQuery("entries").Filter("user", name)
keys, err := q.GetAll(ctx, &entries)
for i, k := range keys {
entries[i].key = k
}
done <- err
}()
success := true
// Wait for the queries to finish in parallel
for i := 0; i < 2 /* count the funcs above */; i++ {
if err := <-done; err != nil {
ctx.Errorf("loaduser: %s", err)
success = false
}
}
if !success {
return
}
// maybe more stuff here
}
This same approach can be used in pretty much any context in which you need to run more than one thing that might take awhile at the same time, whether it's a datastore call, urlfetch, file load, etc.
There is no explicit API for async in Go. You should use go routines instead. I haven't seen any source on this, but I suspect the async API isn't there because of how easy it is to use go routines.
Go's standard library does not have a function solely intended to check if a file exists or not (like Python's os.path.exists). What is the idiomatic way to do it?
To check if a file doesn't exist, equivalent to Python's if not os.path.exists(filename):
if _, err := os.Stat("/path/to/whatever"); errors.Is(err, os.ErrNotExist) {
// path/to/whatever does not exist
}
To check if a file exists, equivalent to Python's if os.path.exists(filename):
Edited: per recent comments
if _, err := os.Stat("/path/to/whatever"); err == nil {
// path/to/whatever exists
} else if errors.Is(err, os.ErrNotExist) {
// path/to/whatever does *not* exist
} else {
// Schrodinger: file may or may not exist. See err for details.
// Therefore, do *NOT* use !os.IsNotExist(err) to test for file existence
}
Answer by Caleb Spare posted in gonuts mailing list.
[...] It's not actually needed very often and [...] using os.Stat is
easy enough for the cases where it is required.
[...] For instance: if you are going to open the file, there's no reason to check whether it exists first. The file could disappear in between checking and opening, and anyway you'll need to check the os.Open error regardless. So you simply call os.IsNotExist(err) after you try
to open the file, and deal with its non-existence there (if that requires special handling).
[...] You don't need to check for the paths existing at all (and you shouldn't).
os.MkdirAll works whether or not the paths already exist. (Also you need to check the error from that call.)
Instead of using os.Create, you should use os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666) . That way you'll get an error if the file already exists. Also this doesn't have a race condition with something else making the file, unlike your version which checks for existence beforehand.
Taken from: https://groups.google.com/forum/#!msg/golang-nuts/Ayx-BMNdMFo/4rL8FFHr8v4J
The first thing to consider is that it is rare that you would only want to check whether or not a file exists. In most situations, you're trying to do something with the file if it exists. In Go, any time you try to perform some operation on a file that doesn't exist, the result should be a specific error (os.ErrNotExist) and the best thing to do is check whether the return err value (e.g. when calling a function like os.OpenFile(...)) is os.ErrNotExist.
The recommended way to do this used to be:
file, err := os.OpenFile(...)
if os.IsNotExist(err) {
// handle the case where the file doesn't exist
}
However, since the addition of errors.Is in Go 1.13 (released in late 2019), the new recommendation is to use errors.Is:
file, err := os.OpenFile(...)
if errors.Is(err, os.ErrNotExist) {
// handle the case where the file doesn't exist
}
It's usually best to avoid using os.Stat to check for the existence of a file before you attempt to do something with it, because it will always be possible for the file to be renamed, deleted, etc. in the window of time before you do something with it.
However, if you're OK with this caveat and you really, truly just want to check whether a file exists without then proceeding to do something useful with it (as a contrived example, let's say that you're writing a pointless CLI tool that tells you whether or not a file exists and then exits ¯\_(ツ)_/¯), then the recommended way to do it would be:
if _, err := os.Stat(filename); errors.Is(err, os.ErrNotExist) {
// file does not exist
} else {
// file exists
}
You should use the os.Stat() and os.IsNotExist() functions as in the following example:
func Exists(name string) (bool, error) {
_, err := os.Stat(name)
if err == nil {
return true, nil
}
if errors.Is(err, os.ErrNotExist) {
return false, nil
}
return false, err
}
edit1: fixed issue of returning true when under some circumstances.
edit2: switched to using errors.Is() from os.IsNotExist(), which many say is a best-practice and here
What other answers missed, is that the path given to the function could actually be a directory. Following function makes sure, that the path is really a file.
func fileExists(filename string) bool {
info, err := os.Stat(filename)
if os.IsNotExist(err) {
return false
}
return !info.IsDir()
}
Another thing to point out: This code could still lead to a race condition, where another thread or process deletes or creates the specified file, while the fileExists function is running.
If you're worried about this, use a lock in your threads, serialize the access to this function or use an inter-process semaphore if multiple applications are involved. If other applications are involved, outside of your control, you're out of luck, I guess.
The example by user11617 is incorrect; it will report that the file exists even in cases where it does not, but there was an error of some other sort.
The signature should be Exists(string) (bool, error). And then, as it happens, the call sites are no better.
The code he wrote would better as:
func Exists(name string) bool {
_, err := os.Stat(name)
return !os.IsNotExist(err)
}
But I suggest this instead:
func Exists(name string) (bool, error) {
_, err := os.Stat(name)
if os.IsNotExist(err) {
return false, nil
}
return err != nil, err
}
_, err := os.Stat(file)
if err == nil {
log.Printf("file %s exists", file)
} else if os.IsNotExist(err) {
log.Printf("file %s not exists", file)
} else {
log.Printf("file %s stat error: %v", file, err)
}
basicly
package main
import (
"fmt"
"os"
)
func fileExists(path string) bool {
_, err := os.Stat(path)
return !os.IsNotExist(err)
}
func main() {
var file string = "foo.txt"
exist := fileExists(file)
if exist {
fmt.Println("file exist")
} else {
fmt.Println("file not exists")
}
}
run example
other way
with os.Open
package main
import (
"fmt"
"os"
)
func fileExists(path string) bool {
_, err := os.Open(path) // For read access.
return err == nil
}
func main() {
fmt.Println(fileExists("d4d.txt"))
}
run it
Best way to check if file exists:
if _, err := os.Stat("/path/to/file"); err == nil || os.IsExist(err) {
// your code here if file exists
}
The function example:
func file_is_exists(f string) bool {
_, err := os.Stat(f)
if os.IsNotExist(err) {
return false
}
return err == nil
}
Let's look at few aspects first, both the function provided by os package of golang are not utilities but error checkers, what do I mean by that is they are just a wrapper to handle errors on cross platform.
So basically if os.Stat if this function doesn't give any error that means the file is existing if it does you need to check what kind of error it is, here comes the use of these two function os.IsNotExist and os.IsExist.
This can be understood as the Stat of the file throwing error because it doesn't exists or is it throwing error because it exist and there is some problem with it.
The parameter that these functions take is of type error, although you might be able to pass nil to it but it wouldn't make sense.
This also points to the fact that IsExist is not same as !IsNotExist, they are way two different things.
So now if you want to know if a given file exist in go, I would prefer the best way is:
if _, err := os.Stat(path/to/file); !os.IsNotExist(err){
//TODO
}
As mentioned in other answers, it is possible to construct the required behaviour / errors from using different flags with os.OpenFile. In fact, os.Create is just a sensible-defaults shorthand for doing so:
// Create creates or truncates the named file. If the file already exists,
// it is truncated. If the file does not exist, it is created with mode 0666
// (before umask). If successful, methods on the returned File can
// be used for I/O; the associated file descriptor has mode O_RDWR.
// If there is an error, it will be of type *PathError.
func Create(name string) (*File, error) {
return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
}
You should combine these flags yourself to get the behaviour you are interested in:
// Flags to OpenFile wrapping those of the underlying system. Not all
// flags may be implemented on a given system.
const (
// Exactly one of O_RDONLY, O_WRONLY, or O_RDWR must be specified.
O_RDONLY int = syscall.O_RDONLY // open the file read-only.
O_WRONLY int = syscall.O_WRONLY // open the file write-only.
O_RDWR int = syscall.O_RDWR // open the file read-write.
// The remaining values may be or'ed in to control behavior.
O_APPEND int = syscall.O_APPEND // append data to the file when writing.
O_CREATE int = syscall.O_CREAT // create a new file if none exists.
O_EXCL int = syscall.O_EXCL // used with O_CREATE, file must not exist.
O_SYNC int = syscall.O_SYNC // open for synchronous I/O.
O_TRUNC int = syscall.O_TRUNC // truncate regular writable file when opened.
)
Depending on what you pick, you will get different errors.
Below is an example which will either truncate an existing file, or fail when a file exists.
openOpts := os.O_RDWR|os.O_CREATE
if truncateWhenExists {
openOpts |= os.O_TRUNC // file will be truncated
} else {
openOpts |= os.O_EXCL // file must not exist
}
f, err := os.OpenFile(filePath, openOpts, 0644)
// ... do stuff
This is how I check if a file exists in Go 1.16
package main
import (
"errors"
"fmt"
"io/fs"
"os"
)
func main () {
if _, err:= os.Stat("/path/to/file"); errors.Is(err, fs.ErrNotExist){
fmt.Print(err.Error())
} else {
fmt.Print("file exists")
}
}
Here is my take on a file exists method. It also checks that the file is not a directory and in case of an error, returns it as well.
// FileExists checks if a file exists (and it is not a directory).
func FileExists(filePath string) (bool, error) {
info, err := os.Stat(filePath)
if err == nil {
return !info.IsDir(), nil
}
if errors.Is(err, os.ErrNotExist) {
return false, nil
}
return false, err
}