diff --git a/util_test.go b/util_test.go
index 76e5396..0b4c763 100644
--- a/util_test.go
+++ b/util_test.go
@@ -1,10 +1,166 @@
 package adb
 
 import (
+	"context"
 	"errors"
+	"net"
+	"os"
+	"path/filepath"
+	"reflect"
+	"sync"
 	"testing"
 )
 
+func withFakeADB(t *testing.T, stdout, stderr string, exitCode string) string {
+	t.Helper()
+
+	tempDir := t.TempDir()
+	argsFile := filepath.Join(tempDir, "args.txt")
+	scriptPath := filepath.Join(tempDir, "adb")
+	script := `#!/bin/sh
+printf '%s\n' "$@" > "$ADB_TEST_ARGS_FILE"
+if [ -n "$ADB_TEST_STDOUT" ]; then
+	printf '%b' "$ADB_TEST_STDOUT"
+fi
+if [ -n "$ADB_TEST_STDERR" ]; then
+	printf '%b' "$ADB_TEST_STDERR" >&2
+fi
+exit "${ADB_TEST_EXITCODE:-0}"
+`
+	if err := os.WriteFile(scriptPath, []byte(script), 0o755); err != nil {
+		t.Fatalf("write fake adb: %v", err)
+	}
+
+	t.Setenv("ADB_TEST_ARGS_FILE", argsFile)
+	t.Setenv("ADB_TEST_STDOUT", stdout)
+	t.Setenv("ADB_TEST_STDERR", stderr)
+	t.Setenv("ADB_TEST_EXITCODE", exitCode)
+
+	t.Setenv("PATH", tempDir+string(os.PathListSeparator)+os.Getenv("PATH"))
+
+	previousADB := adb
+	adb = ""
+	adbOnce = sync.Once{}
+	t.Cleanup(func() {
+		adb = previousADB
+		adbOnce = sync.Once{}
+	})
+
+	return argsFile
+}
+
+func readArgs(t *testing.T, path string) []string {
+	t.Helper()
+	contents, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read args: %v", err)
+	}
+	if len(contents) == 0 {
+		return nil
+	}
+	return splitTrimmedLines(string(contents))
+}
+
+func splitTrimmedLines(in string) []string {
+	lines := []string{}
+	current := ""
+	for _, char := range in {
+		if char == '\n' {
+			if current != "" {
+				lines = append(lines, current)
+			}
+			current = ""
+			continue
+		}
+		current += string(char)
+	}
+	if current != "" {
+		lines = append(lines, current)
+	}
+	return lines
+}
+
+func TestConnect_DefaultPortAndParsedDevice(t *testing.T) {
+	argsFile := withFakeADB(t, "connected to 192.168.1.10:5555\n", "", "0")
+
+	device, err := Connect(context.Background(), ConnOptions{Address: netIP(t, "192.168.1.10")})
+	if err != nil {
+		t.Fatalf("Connect() error = %v", err)
+	}
+
+	wantDevice := Device{
+		SerialNo:     "192.168.1.10:5555",
+		IsAuthorized: true,
+		ConnType:     Network,
+		IP:           netIP(t, "192.168.1.10"),
+		Port:         5555,
+	}
+	if !reflect.DeepEqual(device, wantDevice) {
+		t.Fatalf("Connect() = %#v, want %#v", device, wantDevice)
+	}
+
+	wantArgs := []string{"connect", "192.168.1.10:5555"}
+	if gotArgs := readArgs(t, argsFile); !reflect.DeepEqual(gotArgs, wantArgs) {
+		t.Fatalf("Connect() args = %v, want %v", gotArgs, wantArgs)
+	}
+}
+
+func TestDeviceShell_QuotedArguments(t *testing.T) {
+	argsFile := withFakeADB(t, "", "", "0")
+	device := Device{SerialNo: "SERIAL123"}
+
+	_, _, _, err := device.Shell(context.Background(), `echo "hello world" 'two words'`)
+	if err != nil {
+		t.Fatalf("Shell() error = %v", err)
+	}
+
+	wantArgs := []string{"-s", "SERIAL123", "shell", "echo", "hello world", "two words"}
+	if gotArgs := readArgs(t, argsFile); !reflect.DeepEqual(gotArgs, wantArgs) {
+		t.Fatalf("Shell() args = %v, want %v", gotArgs, wantArgs)
+	}
+}
+
+func TestDeviceRoot_SuccessOutput(t *testing.T) {
+	argsFile := withFakeADB(t, "restarting adbd as root\n", "", "0")
+	device := Device{SerialNo: "SERIAL123"}
+
+	success, err := device.Root(context.Background())
+	if err != nil {
+		t.Fatalf("Root() error = %v", err)
+	}
+	if !success {
+		t.Fatal("Root() success = false, want true")
+	}
+
+	wantArgs := []string{"-s", "SERIAL123", "root"}
+	if gotArgs := readArgs(t, argsFile); !reflect.DeepEqual(gotArgs, wantArgs) {
+		t.Fatalf("Root() args = %v, want %v", gotArgs, wantArgs)
+	}
+}
+
+func TestDeviceDisconnect_UsesDefaultPort(t *testing.T) {
+	argsFile := withFakeADB(t, "", "", "0")
+	device := Device{ConnType: Network, IP: netIP(t, "192.168.1.20")}
+
+	if err := device.Disconnect(context.Background()); err != nil {
+		t.Fatalf("Disconnect() error = %v", err)
+	}
+
+	wantArgs := []string{"disconnect", "192.168.1.20:5555"}
+	if gotArgs := readArgs(t, argsFile); !reflect.DeepEqual(gotArgs, wantArgs) {
+		t.Fatalf("Disconnect() args = %v, want %v", gotArgs, wantArgs)
+	}
+}
+
+func netIP(t *testing.T, address string) net.IPAddr {
+	t.Helper()
+	ip := net.ParseIP(address)
+	if ip == nil {
+		t.Fatalf("parse IP %q", address)
+	}
+	return net.IPAddr{IP: ip}
+}
+
 func Test_filterErr(t *testing.T) {
 	tests := []struct {
 		name    string