Add SelectableFd tests

unittest/vslib/TestSelectableFd.cpp

@@ -0,0 +1,26 @@
+#include "SelectableFd.h"
+
+#include <gtest/gtest.h>
+
+using namespace saivs;
+
+TEST(SelectableFd, ctr)
+{
+    EXPECT_THROW(std::make_shared<SelectableFd>(-1), std::runtime_error);
+
+    SelectableFd fd(0);
+}
+
+TEST(SelectableFd, getFd)
+{
+    SelectableFd fd(7);
+
+    EXPECT_EQ(fd.getFd(), 7);
+}
+
+TEST(SelectableFd, readData)
+{
+    SelectableFd fd(7);
+
+    EXPECT_EQ(fd.readData(), 0);
+}

vslib/SelectableFd.cpp

@@ -9,6 +9,11 @@ SelectableFd::SelectableFd(
 {
     SWSS_LOG_ENTER();
 
+    if (fd < 0)
+    {
+        SWSS_LOG_THROW("invalid file descriptor: %d", fd);
+    }
+
     m_fd = fd;
 }