How to Effectively Test Go Functions Using `log.Fatal()`?

Testing Go Functions Containing log.Fatal()

Consider a scenario where you have a Go function utilizing log.Fatal() to print messages. Testing such functions can be challenging as log.Fatal() triggers os.Exit(1), causing test failures.

Approach:

To overcome this challenge, it's advisable to implement a custom logger that redirects outputs to their standard log.xxx() destinations. However, during testing, you can effortlessly swap functions like log.Fatalf() with your own implementations that do not invoke os.Exit(1).

Example:

Suppose we have the following code that prints logs:

package main

import (
    "log"
)

func hello() {
    log.Print("Hello!")
}

func goodbye() {
    log.Fatal("Goodbye!")
}

func init() {
    log.SetFlags(0)
}

func main() {
    hello()
    goodbye()
}

To test this code, we can formulate hypothetical tests:

package main

import (
    "bytes"
    "log"
    "testing"
)


func TestHello(t *testing.T) {
    var buf bytes.Buffer
    log.SetOutput(&buf)

    hello()

    wantMsg := "Hello!\n"
    msg := buf.String()
    if msg != wantMsg {
        t.Errorf("%#v, wanted %#v", msg, wantMsg)
    }
}

func TestGoodby(t *testing.T) {
    var buf bytes.Buffer
    log.SetOutput(&buf)

    goodbye()

    wantMsg := "Goodbye!\n"
    msg := buf.String()
    if msg != wantMsg {
        t.Errorf("%#v, wanted %#v", msg, wantMsg)
    }
}

Note:

This approach grants flexibility in replacing specific logger functions during testing, allowing for behavior customization without impacting the functionality of the original function being tested.

The above is the detailed content of How to Effectively Test Go Functions Using `log.Fatal()`?. For more information, please follow other related articles on the PHP Chinese website!