diff --git a/engine/resources/net.go b/engine/resources/net.go
index 91130bbb..3dc7d9fe 100644
--- a/engine/resources/net.go
+++ b/engine/resources/net.go
@@ -882,7 +882,11 @@ func (obj *socketSet) nfd() int {
 // and fdPipe. See man select for more info.
 func (obj *socketSet) fdSet() *unix.FdSet {
 	fdSet := &unix.FdSet{}
+	// Generate the bitmask representing the file descriptors in the socketSet.
+	// The rightmost bit corresponds to file descriptor zero, and each bit to
+	// the left represents the next file descriptor number in the sequence of
+	// all real numbers. E.g. the FdSet containing containing 0 and 4 is 10001.
 	fdSet.Bits[obj.fdEvents/64] |= 1 << uint(obj.fdEvents)
-	fdSet.Bits[obj.fdPipe/64] |= 1 << uint(obj.fdPipe) // fd = 3 becomes 100 if we add 5, we get 10100
+	fdSet.Bits[obj.fdPipe/64] |= 1 << uint(obj.fdPipe)
 	return fdSet
 }
diff --git a/engine/resources/net_test.go b/engine/resources/net_test.go
new file mode 100644
index 00000000..ad859192
--- /dev/null
+++ b/engine/resources/net_test.go
@@ -0,0 +1,166 @@
+// Mgmt
+// Copyright (C) 2013-2018+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package resources
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"golang.org/x/sys/unix"
+)
+
+// test cases for NetRes.unitFileContents()
+var unitFileContentsTests = []struct {
+	dev string
+	in  *NetRes
+	out []byte
+}{
+	{
+		"eth0",
+		&NetRes{
+			State:   "up",
+			Addrs:   []string{"192.168.42.13/24"},
+			Gateway: "192.168.42.1",
+		},
+		[]byte(
+			strings.Join(
+				[]string{
+					"[Match]",
+					"Name=eth0",
+					"[Network]",
+					"Address=192.168.42.13/24",
+					"Gateway=192.168.42.1",
+				},
+				"\n"),
+		),
+	},
+	{
+		"wlp5s0",
+		&NetRes{
+			State:   "up",
+			Addrs:   []string{"10.0.2.13/24", "10.0.2.42/24"},
+			Gateway: "10.0.2.1",
+		},
+		[]byte(
+			strings.Join(
+				[]string{
+					"[Match]",
+					"Name=wlp5s0",
+					"[Network]",
+					"Address=10.0.2.13/24",
+					"Address=10.0.2.42/24",
+					"Gateway=10.0.2.1",
+				},
+				"\n"),
+		),
+	},
+}
+
+// test NetRes.unitFileContents()
+func TestUnitFileContents(t *testing.T) {
+	for _, test := range unitFileContentsTests {
+		test.in.SetName(test.dev)
+		result := test.in.unitFileContents()
+		if !bytes.Equal(test.out, result) {
+			t.Errorf("nfd test wanted:\n %s, got:\n %s", test.out, result)
+		}
+	}
+}
+
+// test cases for socketSet.fdSet()
+var fdSetTests = []struct {
+	in  *socketSet
+	out *unix.FdSet
+}{
+	{
+		&socketSet{
+			fdEvents: 3,
+			fdPipe:   4,
+		},
+		&unix.FdSet{
+			Bits: [16]int64{0x18}, // 11000
+		},
+	},
+	{
+		&socketSet{
+			fdEvents: 12,
+			fdPipe:   8,
+		},
+		&unix.FdSet{
+			Bits: [16]int64{0x1100}, // 1000100000000
+		},
+	},
+	{
+		&socketSet{
+			fdEvents: 9,
+			fdPipe:   21,
+		},
+		&unix.FdSet{
+			Bits: [16]int64{0x200200}, // 1000000000001000000000
+		},
+	},
+}
+
+// test socketSet.fdSet()
+func TestFdSet(t *testing.T) {
+	for _, test := range fdSetTests {
+		result := test.in.fdSet()
+		if *result != *test.out {
+			t.Errorf("fdSet test wanted: %b, got: %b", *test.out, *result)
+		}
+	}
+}
+
+// test cases for socketSet.nfd()
+var nfdTests = []struct {
+	in  *socketSet
+	out int
+}{
+	{
+		&socketSet{
+			fdEvents: 3,
+			fdPipe:   4,
+		},
+		5,
+	},
+	{
+		&socketSet{
+			fdEvents: 8,
+			fdPipe:   4,
+		},
+		9,
+	},
+	{
+		&socketSet{
+			fdEvents: 90,
+			fdPipe:   900,
+		},
+		901,
+	},
+}
+
+// test socketSet.nfd()
+func TestNfd(t *testing.T) {
+	for _, test := range nfdTests {
+		result := test.in.nfd()
+		if result != test.out {
+			t.Errorf("nfd test wanted: %d, got: %d", test.out, result)
+		}
+	}
+}