First, to point out the obvious: It is a bad idea to have a test read from
stdin. You should pass a separate io.Reader and use that.
Next: exec.Cmd.{Stdin,Stdout,Stderr} are all set to os.DevNull by default,
meaning you don't get any input or output. I assume
- `go test` does not modify Cmd.Stdin (leaving it at os.DevNull) of the
sub-process it launches and redirects Cmd.{Stdout,Stderr} to buffers.
- Your test (if you use `exec.Command(…).Run()`) also does not modify any
of them, so they stay at os.DevNull
- Other languages have them default to stdin/stdout/stderr of the parent
process, so they try to read from stdin, which is a line-buffered terminal,
so it blocks until you input a line.
Again, the solution here should be to not rely on os.Stdin at all, but
instead test a function which uses a general io.Reader.
On Fri, Nov 5, 2021 at 12:48 PM Amit Saha <amitsaha...@gmail.com> wrote:
>
>
> > On 5 Nov 2021, at 10:27 pm, Amit Saha <amitsaha...@gmail.com> wrote:
> >
> > I have this test function:
> >
> > package main
> >
> > import (
> > "bufio"
> > "fmt"
> > "os"
> > "testing"
> > )
> >
> > func TestInput(t *testing.T) {
> > scanner := bufio.NewScanner(os.Stdin)
> > msg := "Your name please? Press the Enter key when done"
> > fmt.Fprintln(os.Stdout, msg)
> >
> > scanner.Scan()
> > if err := scanner.Err(); err != nil {
> > t.Fatal(err)
> > }
> > name := scanner.Text()
> > if len(name) == 0 {
> > t.Log("empty input")
> > }
> > t.Log(name)
> >
> > }
> >
> > When i run it via go test -v, this is what i get (TLDR; terminates
> without waiting for the interactive input):
> >
> > % go test -v
> >
> > === RUN TestInput
> >
> > Your name please? Press the Enter key when done
> >
> > stdin_test.go:21: empty input
> >
> > stdin_test.go:23:
> >
> > --- PASS: TestInput (0.00s)
> >
> > PASS
> >
> > ok test 0.370s
> >
> >
> >
> > However, when i compile the test and then run the binary, it waits for
> me to enter the input:
> >
> >
> >
> > % go test -c
> >
> > % ./test.test
> >
> > Your name please? Press the Enter key when done
> >
> >
> >
> >
> > The latter behavior is more inline with what i was expecting in the
> first case as well.
> >
> > I thought may be it has something to do with the fact that go test is
> executing the binary (i think) after compiling, and started looking at:
> https://github.com/golang/go/blob/c7f2f51fed15b410dea5f608420858b401887d0a/src/cmd/go/internal/test/test.go
> , but can't see anything obvious.
> >
> > Wondering if anyone of you folks have an answer?
> >
>
> Did a bit more of experimentation, and it seems like, that’s just how
> exec.Command(“mycmd").Run() works.
>
> I tried with exec.Command("wc").Run() and it returns immediately as well.
> (Running the Unix “word count” program).
>
> I suppose I am surprised since in another language I am familiar with
> (Python), a command waiting for an interactive input when executed via
> os/exec would “hang”, for example:
>
> % python3
> Python 3.8.2 (default, Apr 8 2021, 23:19:18)
> [Clang 12.0.5 (clang-1205.0.22.9)] on darwin
> Type "help", "copyright", "credits" or "license" for more information.
> >>> import subprocess
> >>> subprocess.check_output(["wc”])
>
> This will hang
>
> >
> >
> > Thanks,
> >
> > Amit.
> >
> >
> >
> >
> >
> > --
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