Do we need tests for the internal and cmd dirs?

```
$ go test ./...
ok  	go.yaml.in/yaml/v4	2.286s
?   	go.yaml.in/yaml/v4/cmd/go-yaml	[no test files]
?   	go.yaml.in/yaml/v4/internal/libyaml	[no test files]
ok  	go.yaml.in/yaml/v4/internal/testutil/assert	(cached)
ok  	go.yaml.in/yaml/v4/yts	0.099s
```

Also should make test trigger `go test ./...` instead of just `go test`?