gocover

Overview

gocover is a go unit test coverage explorer and inspector, providing go module level test coverage based on go test coverage result, as well as diff coverage between git commits. Plus, the tool supports annotations of ignoring file/blocks at coverage calculation stage.

Installation

Install From Release

• Download the latest Release and extract it.

Install From Source

• Clone the repo
• Build Binary

go build .

Usage

Definition

Here is how we inspect the test coverage:

• Total Lines: # of total lines of your change or the entire repo/module
• Ignored Lines: # of the lines you ignored
• Effictive Lines: total lines - ignored lines
• Covered Lines: # of the lines covered by test
• Coverage: Covered Lines / Effictive Lines

Run Coverage Check

• Run test and get coverage.out

go test ./... -coverprofile=coverage.out

• Get diff coverage

You need to commit the change to your branch before running go test.

gocover diff --repository-path=${REPO ROOT PATH} --cover-profile=${PATH TO}coverage.out --compare-branch=origin/master 

• Get overall coverage

gocover full --repository-path=${REPO ROOT PATH} --cover-profile=${PATH TO}coverage.out

• Check the coverage detail at coverage.html

• Note: Before the coverage inspection, we will check whether a _test.go file exist within each package.

Run unit test and get coverage results in one command

Use following command to run the unit tests and get coverage on the module. The cover profiles and coverage result are written in the output directory.

• --executor-mode, what test framework to run the unit tests. go uses go test ./... -coverpkg=./..., ginkgo uses -p -r -trace -cover -coverpkg ./... ./ to run the unit tests.
• --excludes, exclude the files that match the exclude patterns, the excluded files won't be used to calculate coverage result.

gocover test --repository-path=${REPO ROOT PATH} --coverage-mode [full|diff] --executor-mode [go|ginkgo] --excludes '**/mock_*/**' --outputdir /tmp

For the project has multiple module, please specify module-dir to generates the coverage for the module. module-dir flag is the relative path to the root of the project.

Set Ignore Annotations

Use //+gocover:ignore:file comments or //+gocover:ignore:block comments as annotation, do not add any space among words, and adding non-empty comments. Note that comments does not support multiple lines.

Ignore files

Put //+gocover:ignore:file comments at any line in a file to ignore a file at coverage inspection. Note that //+gocover:ignore:file comments has the highest priority, it will overrides other ignoring annotation.

//+gocover:ignore:file ignore this file!
package foo
func foo() {}

Ignore Block

We follow the definition of basic block from go test to keep the same logic on coverage calculation.

• Note: The block is different from the golang block. If you are not sure about the definition of the block, you can check the detail about every block within your change at the coverage.out file. Make sure to put the annotation into the block.
• Note: As we use # of lines in coverage calculation, there is a special case that a single line falling into several blocks. In this case, if any part of a line falls into an ignored block, the line will be regard as an ignored line. You can check it at function case5 in the following examples.

package main

import "fmt"

var i, j int = 1, 2

func case1() { //+gocover:ignore:block ignore this block  -|
 var c, python, java = true, false, "no!"               // | -> Lines ignored
 fmt.Println(i, j, c, python, java)                     //-|
}

func case2(x int) {//+gocover:ignore:block ignore this block  -|
 var c, python, java = true, false, "no!"                   // | -> Lines ignored
 if x > 0 {                                                 //-|
  fmt.Println(i, j, c, python, java)
 }

 fmt.Println(i, j, c, python, java, x)
}

func case3(x int) {//+gocover:ignore:block ignore this block -|
 var c, python, java = true, false, "no!"                  // | -> Lines ingored - Block1
 if x > 0 { //+gocover:ignore:block ignore this block        -|
  fmt.Println(i, j, c, python, java)                       // | -> Lines ingored - Block2
 }                                                         //-|

 fmt.Println(i, j, c, python, java, x)
}

func case4(func() int) {
	{ //+gocover:ignore:block ignore this block      -|
		fmt.Printf("A")                        // |
		fmt.Printf("A")                        // | -> Lines ignored
		fmt.Printf("A")                        // |
	}                                              //-|
	fmt.Printf("A")
}

func case5(x int) {                                //-|
	//+gocover:ignore:block ignore this block     | 
	case6(func() int {                         //-| -> Lines ignored
		return 1
	})
}

Advanced Usage

Commands

Command Options	Definition
--cover-profile	Coverage profile produced by 'go test’
--repository-path	The root path of repository
--module-dir	Relative directory to the root repository path that contains go.mod file
--timeout	Execute timeout in seconds, default is 3600

• Diff Coverage

Command Options	Definition
--branch-to-compare	branch to compare
--coverage-baseline	The tool will return an error code if coverage is less than coverage baseline(%)
--output	Diff coverage output file
--format	Format of the diff coverage report, one of: html, json, markdown
--excludes	Exclude files for diff coverage inspection

FAQ

How to run gocover in a multiple module repository

1. Change the working directory to the module.
2. Set --module-dir flag to the relative directory of the module
3. Set --repository-path flag to the absolutely path of the repository or a relative path to the working directory.

For example, the directory tree is as following, and the repository path is /home/user/s

.
├── modulea
│   └── go.mod
└── moduleb
    └── go.mod

So you can run the gocover on modulea as following:

cd modulea
gocover test --repository-path /home/user/s --module-dir modulea 
# or
gocover test --repository-path ../ --module-dir modulea 

How to calculate diff coverage

There are mainly there steps to calculate diff coverage for a module.

1. Use go test to generate cover profiles for the module because gocover highly relies on cover profiles generated by it.
2. Generate git diff changes compared current branch with master/main branch.
3. Loop over each line from the diff changes, and reverse lookup the profile block from the cover profile in the step 1. The Count field of cover profile indicates whether this code line is covered by unit test or not.

Package Coverage Rule

1. gocover relies on go cover to generate test coverage
2. go cover relies on _test.go under a package to calculate coverage for the package (not crossing the package)
3. if we don't care about the test coverage for a package, it's fine to have no _test.go under the package. In this situation, package owner is responsible for the quality of this package.
4. if we want to count the package into test coverage, we should at least create one _test.go under the package

For example, there are two package, pkga and pkgb, and pkgb reference a function of pkga. Following is the output of the go test.

.
├── coverage.out
├── go.mod
├── pkga
│   └── a.go
└── pkgb
    ├── b.go
    └── b_test.go

$ go test ./... -coverprofile=coverage.out
?       gotest  [no test files]
?       gotest/pkga     [no test files]
ok      gotest/pkgb     0.002s  coverage: 0.0% of statements [no tests to run]

$ cat coverage.out
mode: set
gotest/pkgb/b.go:8.17,10.2 1 0

If a package needs diff coverage result, please make sure that a least one _test.go exists, even though its contents are emtpy. The empty _test.go means it's only a valid _test.go.

package a

or

package a

import "testing"

func TestFoo(t *testing.T) {

}

Contributing

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This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact [email protected] with any additional questions or comments.

Trademarks

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