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How to test the passing of arguments in Golang?

package main

import (
    "flag"
    "fmt"
)

func main() {
    passArguments()
}

func passArguments() string {
    username := flag.String("user", "root", "Username for this server")
    flag.Parse()
    fmt.Printf("Your username is %q.", *username)

    usernameToString := *username
    return usernameToString
}

Passing an argument to the compiled code:

./args -user=bla

results in:

Your username is "bla"

the username that has been passed is displayed.


Aim: in order to prevent that the code needs to be build and run manually every time to test the code the aim is to write a test that is able to test the passing of arguments.


Attempt

Running the following test:

package main

import (
    "os"
    "testing"
)

func TestArgs(t *testing.T) {
    expected := "bla"
    os.Args = []string{"-user=bla"}

    actual := passArguments()

    if actual != expected {
        t.Errorf("Test failed, expected: '%s', got:  '%s'", expected, actual)
    }
}

results in:

Your username is "root".Your username is "root".--- FAIL: TestArgs (0.00s)
    args_test.go:15: Test failed, expected: 'bla', got:  'root'
FAIL
coverage: 87.5% of statements
FAIL    tool    0.008s

Problem

It looks like that the os.Args = []string{"-user=bla is not able to pass this argument to the function as the outcome is root instead of bla

like image 541
030 Avatar asked Nov 15 '15 18:11

030


People also ask

How do you pass arguments in Golang?

Command-line arguments are a way to provide the parameters or arguments to the main function of a program. Similarly, In Go, we use this technique to pass the arguments at the run time of a program. In Golang, we have a package called as os package that contains an array called as “Args”.

How do you run a test in Golang?

At the command line in the greetings directory, run the go test command to execute the test. The go test command executes test functions (whose names begin with Test ) in test files (whose names end with _test.go). You can add the -v flag to get verbose output that lists all of the tests and their results.


1 Answers

Per my comment, the very first value in os.Args is a (path to) executable itself, so os.Args = []string{"cmd", "-user=bla"} should fix your issue. You can take a look at flag test from the standard package where they're doing something similar.

Also, as os.Args is a "global variable", it might be a good idea to keep the state from before the test and restore it after. Similarly to the linked test:

oldArgs := os.Args
defer func() { os.Args = oldArgs }()

This might be useful where other tests are, for example, examining the real arguments passed when evoking go test.

like image 143
tomasz Avatar answered Oct 01 '22 13:10

tomasz