GOBCO - Golang Branch Coverage

Gobco measures branch coverage of Go code.

Gobco should be used in addition to go test -cover, rather than replacing it. 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/rillig/gobco@latest

With go1.16 or older:

$ go get github.com/rillig/gobco

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 netbsd.org/pkglint:

=== RUN   Test
OK: 756 passed
--- PASS: Test (16.56s)
PASS
Branch coverage: 5452/6046
alternatives.go:28:32: condition "G.Pkg.vars.Defined(\"ALTERNATIVES_SRC\")" was 11 times false but never true
autofix.go:98:6: condition "rawLine.Lineno != 0" was 245 times true but never false
autofix.go:390:12: condition "fix.line.firstLine >= 1" was 392 times true but never false
buildlink3.go:22:5: condition "trace.Tracing" was 19 times true but never false
...
substcontext.go:136:22: condition "(value == \"pre-configure\" || value == \"post-configure\")" was once true but never false
substcontext.go:136:23: condition "value == \"pre-configure\"" was once true but never false
substcontext.go:136:51: condition "value == \"post-configure\"" was never evaluated

Even if some tests still fail, gobco can compute the code coverage:

$ gobco sample/foo.go
--- FAIL: TestFoo (0.00s)
    foo_test.go:7: wrong
FAIL
FAIL    github.com/rillig/gobco/sample  0.315s
FAIL
exit status 1

Branch coverage: 5/6
sample\foo.go:10:5: condition "Bar(a) == 10" was once false but never true

Adding custom test conditions

If you want to ensure that a certain condition in your code is covered by the tests, you can insert the desired condition into the code and just 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.

Since the above conditions are syntactically recognizable as boolean expressions, gobco inserts its coverage code around them.

Note that for boolean expressions that don't clearly look like boolean expressions, you have to write cond == true instead of a simple cond since as of March 2021, gobco only analyzes the code at the syntactical level, without resolving any types.