How to test the passing of arguments in Golang?

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