actions-demo

A deliberately small Go CLI whose only real job is to give a GitHub Actions demo something to build, test, and occasionally fall over on. There are two tiny packages under internal/, a thin command-line wrapper in main.go, and a CI workflow that lints, tests across two Go versions, and then builds and smoke-tests the resulting binary.

Building and running

$ go build -o actions-demo .
$ ./actions-demo add 2 3
5
$ ./actions-demo palindrome "A man, a plan, a canal: Panama"
true
$ ./actions-demo title "hello wide world"
Hello Wide World

Run ./actions-demo help for the full list of commands.

Running the tests

$ go test ./...
$ go test -race -coverprofile=coverage.out ./... && go tool cover -func=coverage.out

The CI workflow

.github/workflows/ci.yml runs on every push and pull request against main, and can also be triggered by hand from the Actions tab. It has three jobs:

• Lint, which fails if anything is not gofmt'd, and then runs go vet.
• Test, a matrix across Go 1.25 and the current stable release, running the tests with the race detector and printing a coverage summary.
• Build, which depends on the other two, compiles the binary, and smoke tests it by checking that add 2 3 really does return 5.

Breaking it on purpose

The whole point of this repository is that it can be broken and unbroken in a single edit, so here are a few reliable ways to do that, in rough order of how quickly the failure shows up.

What to change	Which job fails	What you will see
In internal/calc/calc.go, make Add return a - b	Test, then Build	Four subtests of TestAdd fail, along with the add case in TestRunCommands
In internal/calc/calc.go, drop the b == 0 guard in Divide	Test	TestDivideByZero fails, and the CLI panics with an integer divide by zero
In internal/textutil/textutil.go, change Reverse to iterate over []byte rather than []rune	Test	Only the multi-byte case fails, which is a nice illustration of a test earning its keep
In internal/textutil/textutil.go, remove the unicode.IsDigit check in Normalise	Test	TestNormalise fails on the digits case whilst everything else passes
Add a stray if x := 1; x == 1 { with an unused variable, or an unreachable return	Lint	go vet complains before the tests ever run
Indent something with spaces instead of a tab	Lint	The gofmt -l step lists the offending file
In internal/calc/calc.go, make Max start from 0 rather than values[0]	Test	Only the all-negative case fails

The last two are particularly useful if you want to show the difference between a failure that a formatter can fix mechanically and one that needs somebody to think about the logic.

To unbreak, revert the edit; git checkout -- . or git revert both work, and pushing the fix will turn the badge green again within a minute or so.