What version of Go are you using (go version)?

$ go version
go1.14

Does this issue reproduce with the latest release?

Yes and tip as well.

What operating system and processor architecture are you using (go env)?

Not revelant.

What did you do?

Visited https://golang.org/pkg/errors/#example_As.

Then visited https://godoc.org/errors#example-As and https://pkg.go.dev/errors/?tab=doc#example-As to compare, same problem.

What did you expect to see?

As per documented in https://golang.org/pkg/testing/#hdr-Examples (emphasis mine):

The entire test file is presented as the example when it contains a single example function, at least one other function, type, variable, or constant declaration, and no test or benchmark functions.

I expected to see the example for using errors.As, a rather small snippet containing:

   if _, err := os.Open("non-existing"); err != nil {
        var pathError *os.PathError
        if errors.As(err, &pathError) {
            fmt.Println("Failed at path:", pathError.Path)
        } else {
            fmt.Println(err)
        }
    }

As defined in https://golang.org/src/errors/wrap_test.go?s=4623:4893#L241.

What did you see instead?

A large amount of code containing tests defined in https://golang.org/src/errors/wrap_test.go, with the actual example code transformed into a func main at the very bottom.