Add basic Select tests

[walles]

And Linux CI.

The background here is that I believe Select is broken on Windows.

After this PR is merged I want to add Windows CI as well to prove / disprove that.

Ref: https://github.com/walles/moar/issues/222

I noticed CI isn't running though, maybe GitHub Actions has to be enabled in the project settings or something?

[walles]

@artbin, would it be possible for you do go test in this branch on Windows?

I'm super interested in whether the tests pass there!

[creack]

TestSelect_readEmptyPipe fails with The pipe has bytes, should have been ready for reading

Note that TestReadWriteSync fails as well (and fails in master too).

[walles]

@creack on which platform did all tests fail for you?

I tested on macOS and Linux and they all passed.

[walles]

Linux, in Docker:

root@68308311032f:/goselect# go test -v ./...
?   	github.com/creack/goselect/example	[no test files]
=== RUN   TestReadWriteSync
--- PASS: TestReadWriteSync (1.54s)
=== RUN   TestSelect_readEmptyPipe
--- PASS: TestSelect_readEmptyPipe (0.01s)
=== RUN   TestSelect_readClosedPipe
--- PASS: TestSelect_readClosedPipe (0.00s)
=== RUN   TestSelect_readWrittenPipe
--- PASS: TestSelect_readWrittenPipe (0.00s)
PASS
ok  	github.com/creack/goselect	1.555s
root@68308311032f:/goselect#

macOS:

~/s/goselect (johan/add-tests|✔) $ go test -v ./...
=== RUN   TestReadWriteSync
--- PASS: TestReadWriteSync (1.54s)
=== RUN   TestSelect_readEmptyPipe
--- PASS: TestSelect_readEmptyPipe (0.01s)
=== RUN   TestSelect_readClosedPipe
--- PASS: TestSelect_readClosedPipe (0.00s)
=== RUN   TestSelect_readWrittenPipe
--- PASS: TestSelect_readWrittenPipe (0.00s)
PASS
ok  	github.com/creack/goselect	(cached)
?   	github.com/creack/goselect/example	[no test files]
~/s/goselect (johan/add-tests|✔) $

[creack]

on windows 10

[walles]

TestSelect_readEmptyPipe fails with The pipe has bytes, should have been ready for reading

Is the test doing something wrong? Or is the Windows specific code broken?

func TestSelect_readEmptyPipe(t *testing.T) {
	r, w, err := os.Pipe()
	if err != nil {
		t.Fatal(err)
	}
	defer func() {
		if err := w.Close(); err != nil {
			t.Fatal(err)
		}
		if err := r.Close(); err != nil {
			t.Fatal(err)
		}
	}()

	rFDSet := &FDSet{}
	rFDSet.Set(r.Fd())
	max := r.Fd()
	if err := Select(int(max+1), rFDSet, nil, nil, 10*time.Millisecond); err != nil {
		t.Fatalf("select call failed: %s", err)
	}

	if rFDSet.IsSet(r.Fd()) {
		t.Fatal("Nothing written, the pipe should not have been ready for reading")
	}
}

[walles]

Having this PR open provides no value, closing.

As long as goselect doesn't work on Windows these tests won't pass, and this PR can't be merged.