Golang Test Coverage

This document summarizes how to check Test Coverage in Golang.

1. Golang Test Coverage

Golang provides functionality to check Test Code Coverage. Here, Coverage means Coverage called Statement Coverage or Line Coverage. Statement Coverage means Coverage that is satisfied when one line of Code is executed at least once.

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{% highlight golang %}
package coverage

func TestFunc(n int) int {
	if n < 0 {
		return -1
	} else if n == 0 {
		return 0
	} else {
		return 1
	}
}

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package coverage

import (
	"testing"
)

func TestCover(t *testing.T) {
	result := TestFunc(-1)
	if result != -1 {
		t.Error("Wrong result")
	}

	result = TestFunc(0)
	if result != 0 {
		t.Error("Wrong result")
	}
}

[Code 1] shows a simple function testFunc() for testing, and [Code 2] shows simple Test Code using the testFunct() function from [Code 1].

1.1. Test with Coverage

$ go test -cover .                   
ok      ssup2.com/test  0.001s  coverage: 80.0% of statements

[Shell 1] shows checking Package-level Coverage using the cover Option when performing Tests from [Code 2]. You can check Package-level Coverage through the cover Option.

1.2. Test with Coverage Profile

$ go test -coverprofile cover.prof ./...
ok      ssup2.com/test  0.001s  coverage: 80.0% of statements

$ go tool cover -html=cover.prof -o cover.html

When you want to check Code-level Coverage in detail, you can create and use a Coverage Profile. [Shell 2] shows creating a Coverage Profile using the coverprofile Option when performing Tests from [Code 2].

The created Coverage Profile can be converted to an HTML file through the go tool cover command, and you can easily check Coverage in a Web Browser using the converted HTML file. [Figure 1] shows the generated HTML from [Code 2]. Since the Test Code does not have cases where n is greater than 1, the last part of the testFunc() function is not executed, so you can see that Coverage does not reach 100%. You can check Coverage by file.

2. References

• https://err0rcode7.github.io/backend/2021/05/11/%ED%85%8C%EC%8A%A4%ED%8A%B8%EC%BB%A4%EB%B2%84%EB%A6%AC%EC%A7%80.html