## How to Achieve 100% Code Coverage Without Blind Spots When Using os.Exit()?

Showing Coverage of Functional Tests Without Blind Spots

In software testing, code coverage measures the percentage of code that is executed during tests. However, it's possible that certain code paths are not covered, creating blind spots in the coverage report. One such scenario arises when using a binary compiled from production code for functional testing.

Consider the following example:

<code class="go">package main

import (
    "fmt"
    "math/rand"
    "os"
    "time"
)

func main() {
    rand.Seed(time.Now().UTC().UnixNano())
    for {
        i := rand.Int()
        fmt.Println(i)
        if i%3 == 0 {
            os.Exit(0)
        }
        if i%2 == 0 {
            os.Exit(1)
        }
        time.Sleep(time.Second)
    }
}</code>

The Problem:

The exit() function exits the process without allowing the coverage profile to be written. Consequently, the line containing os.Exit() is not covered in the coverage report, creating a blind spot.

Potential Solutions:

1. Avoid Using os.Exit() in Test Code:

Move the exit functionality into a separate function and use that function in both the production and test code. This allows the coverage profile to be captured before exiting.

2. Use a time.Sleep() Before Exiting:

Insert a time.Sleep() delay before calling os.Exit() to allow the cover profile to be written, but this can slow down the production code if the binary is used for both production and testing.

3. Exclude Main Function from Coverage:

Since the main function only exits the process, it can be excluded from coverage analysis using build tags. This ensures that the blind spot is eliminated.

Example Refactoring:

<code class="go">package main

import (
    "fmt"
    "math/rand"
    "os"
    "time"
)

//+build !test

func main() {
    os.Exit(exitFunc())
}

func exitFunc() int {
    rand.Seed(time.Now().UTC().UnixNano())
    for {
        i := rand.Int()
        fmt.Println(i)
        if i%3 == 0 {
            return 0 // Exit with code 0
        }
        if i%2 == 0 {
            fmt.Println("status 1")
            return 1 // Exit with code 1
        }
        time.Sleep(time.Second)
    }
}</code>

By excluding the main function from coverage, we achieve 100% coverage without any blind spots.

Note:

For complex scenarios, it's recommended to consult with experienced developers to determine the best approach for eliminating coverage blind spots without compromising code functionality or test efficiency.

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