add basic systemd service monitoring (#1153)

Co-authored-by: Shelby Tucker <shelby.tucker@gmail.com>

agent/systemd_test.go

@@ -0,0 +1,48 @@
+//go:build linux && testing
+
+package agent
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUnescapeServiceName(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"nginx.service", "nginx.service"},                                     // No escaping needed
+		{"test\\x2dwith\\x2ddashes.service", "test-with-dashes.service"},       // \x2d is dash
+		{"service\\x20with\\x20spaces.service", "service with spaces.service"}, // \x20 is space
+		{"mixed\\x2dand\\x2dnormal", "mixed-and-normal"},                       // Mixed escaped and normal
+		{"no-escape-here", "no-escape-here"},                                   // No escape sequences
+		{"", ""},                                                               // Empty string
+		{"\\x2d\\x2d", "--"},                                                   // Multiple escapes
+	}
+
+	for _, test := range tests {
+		t.Run(test.input, func(t *testing.T) {
+			result := unescapeServiceName(test.input)
+			assert.Equal(t, test.expected, result)
+		})
+	}
+}
+
+func TestUnescapeServiceNameInvalid(t *testing.T) {
+	// Test invalid escape sequences - should return original string
+	invalidInputs := []string{
+		"invalid\\x",   // Incomplete escape
+		"invalid\\xZZ", // Invalid hex
+		"invalid\\x2",  // Incomplete hex
+		"invalid\\xyz", // Not a valid escape
+	}
+
+	for _, input := range invalidInputs {
+		t.Run(input, func(t *testing.T) {
+			result := unescapeServiceName(input)
+			assert.Equal(t, input, result, "Invalid escape sequences should return original string")
+		})
+	}
+}