## How to Achieve Complete Coverage in Functional Tests: Bridging the Gap Between Code and Execution?

How to Show Complete Coverage in Functional Tests

Problem:

Functional tests execute compiled binary code, leaving room for uncovered blind spots.

Code Snippet:

<code class="go">package main

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

var exitCode int

func Test_main(t *testing.T) {
    go main()
    exitCode = <-exitCh
}

func TestMain(m *testing.M) {
    m.Run()
    // can exit because cover profile is already written
    os.Exit(exitCode)
}

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>

Solution:

1. Exclude Main Function Using Build Tags:

<code class="go">//+build !test

package main

func main() {
    os.Exit(doFunc());
}</code>

Build with tags:

go test -c -coverpkg=. -o example -tags test

2. Extract Functionality to Testable Code:

Avoid testing the main function by extracting functionality into other classes. Use func TestMain to control code execution on the main thread.

3. Use Mocking:

Create mocks for dependencies to isolate specific code paths and improve testability.

4. Timeouts for Coverage:

Add a timeout to the test to give the coverage tool time to write the profile before the application exits.

Example with Timeouts:

<code class="go">func exit(code int) {
    exitCh <- code
    time.Sleep(1 * time.Second) // Allow time for coverage data to be written
    os.Exit(code)
}</code>

Benefits:

• Uncovered blind spots in functional test coverage
• Improved testability and maintainability of production code
• Confidence in the accuracy and completeness of coverage reports

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