gobco

GOBCO - Golang Branch Coverage

Gobco measures condition coverage of Go code.

Gobco is intended to be used in addition to go test -cover. For example, gobco does not detect functions or methods that are completely unused, it only notices them if they contain any conditions or branches. Gobco also doesn't cover select statements.

Installation

With go1.17 or later:

$ go install github.com/IssacRunmin/gobco@latest

Older go releases are not supported.

Usage

To run gobco on a single package, run it in the package directory:

$ gobco

The output typically looks like the following example, taken from package github.com/rillig/pkglint:

ok  	github.com/rillig/pkglint/v23	29.648s

Condition coverage: 8720/8840
...
changes.go:171:61: condition "n == 6" was 12 times true but never false
distinfo.go:268:8: condition "alg == \"SHA1\"" was 16 times false but never true
distinfo.go:322:13: condition "remainingHashes[0].algorithm == alg" was 8 times true but never false
...
mkcondsimplifier.go:141:31: condition "p[2] == p[1]-'A'+'a'" was 26 times true but never false
...
vartypecheck.go:1027:11: condition "len(invalid) > 1" was once false but never true
vartypecheck.go:1628:42: condition "cv.MkLines.pkg != nil" was 8 times true but never false
vartypecheck.go:1630:6: condition "distname.IsConstant()" was 8 times true but never false

To run gobco on multiple packages with branch coverage enabled, use:

$ gobco -branch ./...

The output (with -list-all) typically looks like the following example, taken from testdata/multi-pkgs:

ok      demo    0.389s [no tests to run]
ok      demo/bar        0.363s
ok      demo/foo        0.340s

Branch coverage: 2/2

Branch coverage: 2/2
bar/bar.go:4:5: condition "x > 0" was once true and once false

Adding custom test conditions

If you want to ensure that the tests cover a certain condition in your code, you can insert the desired condition into the code and assign it to the underscore:

func square(x int) int {
    _ = x > 50
    _ = x == 0
    _ = x < 0

    return x * x
}

The compiler will see that these conditions are side-effect-free and will thus optimize them away, so there is no runtime overhead.

Gobco only inserts its coverage code around expressions that are syntactically recognizable as boolean expressions, such as comparisons, '&&', '||', '!'. When a boolean expression is merely passed around, there is no branch involved, thus nothing to do for branch coverage.