add basic systemd service monitoring (#1153)

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

internal/hub/systems/system_systemd_test.go

@@ -0,0 +1,75 @@
+//go:build testing
+
+package systems
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetSystemdServiceId(t *testing.T) {
+	t.Run("deterministic output", func(t *testing.T) {
+		systemId := "sys-123"
+		serviceName := "nginx.service"
+
+		// Call multiple times and ensure same result
+		id1 := getSystemdServiceId(systemId, serviceName)
+		id2 := getSystemdServiceId(systemId, serviceName)
+		id3 := getSystemdServiceId(systemId, serviceName)
+
+		assert.Equal(t, id1, id2)
+		assert.Equal(t, id2, id3)
+		assert.NotEmpty(t, id1)
+	})
+
+	t.Run("different inputs produce different ids", func(t *testing.T) {
+		systemId1 := "sys-123"
+		systemId2 := "sys-456"
+		serviceName1 := "nginx.service"
+		serviceName2 := "apache.service"
+
+		id1 := getSystemdServiceId(systemId1, serviceName1)
+		id2 := getSystemdServiceId(systemId2, serviceName1)
+		id3 := getSystemdServiceId(systemId1, serviceName2)
+		id4 := getSystemdServiceId(systemId2, serviceName2)
+
+		// All IDs should be different
+		assert.NotEqual(t, id1, id2)
+		assert.NotEqual(t, id1, id3)
+		assert.NotEqual(t, id1, id4)
+		assert.NotEqual(t, id2, id3)
+		assert.NotEqual(t, id2, id4)
+		assert.NotEqual(t, id3, id4)
+	})
+
+	t.Run("consistent length", func(t *testing.T) {
+		testCases := []struct {
+			systemId    string
+			serviceName string
+		}{
+			{"short", "short.service"},
+			{"very-long-system-id-that-might-be-used-in-practice", "very-long-service-name.service"},
+			{"", "empty-system.service"},
+			{"empty-service", ""},
+			{"", ""},
+		}
+
+		for _, tc := range testCases {
+			id := getSystemdServiceId(tc.systemId, tc.serviceName)
+			// FNV-32 produces 8 hex characters
+			assert.Len(t, id, 8, "ID should be 8 characters for systemId='%s', serviceName='%s'", tc.systemId, tc.serviceName)
+		}
+	})
+
+	t.Run("hexadecimal output", func(t *testing.T) {
+		id := getSystemdServiceId("test-system", "test-service")
+		assert.NotEmpty(t, id)
+
+		// Should only contain hexadecimal characters
+		for _, char := range id {
+			assert.True(t, (char >= '0' && char <= '9') || (char >= 'a' && char <= 'f'),
+				"ID should only contain hexadecimal characters, got: %s", id)
+		}
+	})
+}