add FindProcess for posix

Signed-off-by: leongross <leon.gross@9elements.com>

src/os/exec_test.go

@@ -0,0 +1,32 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os_test
+
+import (
+	. "os"
+	"runtime"
+	"testing"
+)
+
+func TestFindProcess(t *testing.T) {
+	// NOTE: For now, we only test the Linux case since only exec_posix.go is currently the only implementation.
+	if runtime.GOOS == "linux" {
+		// Linux guarantees that there is pid 0
+		proc, err := FindProcess(0)
+		if err != nil {
+			t.Error("FindProcess(0): wanted err == nil, got %v:", err)
+		}
+
+		if proc.Pid != 0 {
+			t.Error("Expected pid 0, got: ", proc.Pid)
+		}
+
+		pid0 := Process{Pid: 0}
+		if *proc != pid0 {
+			t.Error("Expected &Process{Pid: 0}, got", *proc)
+		}
+	}
+
+}