go test that fails on untested lines and shows them

• 🎉 Instant and actionable feedback on 💚 test run
• 🚀 Fast PRs: avoid comments and CI failures
• 💰 No 3rd-party payment / integration / security-leaks
• Highlight untested code sections with inline // untested section comment
• Onboard untested code (top of the file // untested sections: 5 comment)
• Ignore untested files (top of the file // untested sections: ignore comment)
• Run ginko with go-testcov ginko ./...

go get github.com/grosser/go-testcov
go-testcov . # same arguments as `go test` uses, so for example `go-testcov ./...` for everything
...
test output
...
pkg.go new untested sections introduced (2 current vs 0 configured)
pkg.go:20.14,21.11
pkg.go:54.5,56.5

• Docs for coverage in go
• Runtime overhead for coverage is about 3%
• Use -covermode atomic when testing parallel algorithms
• To keep the coverage.out file run with -cover
• go-testcov version to see current version

.PHONY: test
test: go-testcov ## Unit test
	$(GOTESTCOV) ./... -covermode atomic

LOCALBIN ?= $(shell pwd)/bin
$(LOCALBIN):
	mkdir -p $(LOCALBIN)
GOTESTCOV ?= $(LOCALBIN)/go-testcov
GOTESTCOV_VERSION ?= v1.10.0

.PHONY: go-testcov
go-testcov: $(LOCALBIN) # Download go-testcov (replace existing if incorrect version)
	@(test -f $(GOTESTCOV) && $(GOTESTCOV) version | grep "$(GOTESTCOV_VERSION)" >/dev/null) || \
	(rm -f $(GOTESTCOV) && echo "Installing $(GOTESTCOV) $(GOTESTCOV_VERSION)" && \
	GOBIN=$(LOCALBIN) go install github.com/grosser/go-testcov@$(GOTESTCOV_VERSION))

graph TD;
GoTestCov(go-testcov .)
GoTest(go test . -cover --coverprofile coverage.out)
Coverage(coverage.out)
GoTestCov--runs-->GoTest;
GoTest--produces-->Coverage;
GoTestCov--parses-->Coverage;

coverage.out shows the coverage of each file "section".

A "section" is a chunk of uninterrupted code, for example:

func main() {
  if foo(1) {
      fmt.Print("Hi")
  }
  fmt.Print("Ho")
}

has 3 sections:

github.com/foo/bar/main.go:1.13,2.13 1 1
github.com/foo/bar/main.go:2.13,3.4 1 1
github.com/foo/bar/main.go:5.3,5.18 1 1

1. 1.13,2.13: after opening main() { until after if foo(1) {
2. 2.13,3.4: after if foo(1) { until after if closing }
3. 5.3,5.18: fmt.Print("Ho")

• the else case (aka "what if foo(1) returns false") has no coverage information
• when not using modules the path is /full/path/to/main.go

Run go-testcov on itself:

make

• all tests are in test/ so the main library does not force installation of gomega + ginkgo
• the files from the root folder are symlinked there to make everything load
• easiest to work from that folder directly

• make new version commit that changes version in readme "Makefile setup" + main.go
• push and tag the commit

Michael Grosser
[email protected]
License: MIT