refactor: Introduce constants for common string literals and improve type assertion safety in tests.

Author: sumant1122

internal/config/config.go

@@ -141,10 +141,12 @@ func missingHint(cmd, title string) string {
 	return fmt.Sprintf("Missing %s. Install the command to enable this tab.", cmd)
 }
 
+const osDarwin = "darwin"
+
 func buildDefaultTabs() []Tab {
 	freeCmd := []string{"free", "-m"}
 	freeTitle := "free -m"
-	if runtime.GOOS == "darwin" {
+	if runtime.GOOS == osDarwin {
 		freeCmd = []string{"vm_stat"}
 		freeTitle = "vm_stat (free)"
 	}

internal/monitor/monitor.go

@@ -35,7 +35,12 @@ type SystemInfo struct {
 	Net    string
 }
 
-const HistoryLength = 30
+const (
+	HistoryLength = 30
+	unknownStr    = "unknown"
+	loStr         = "lo"
+	lo0Str        = "lo0"
+)
 
 func UpdateHistory(history MetricHistory, sample MetricsSample) MetricHistory {
 	if sample.OkLoad {
@@ -137,16 +142,16 @@ func FormatRate(kbPerSec float64) string {
 
 func getUptimeShort() string {
 	if _, err := exec.LookPath("uptime"); err != nil {
-		return "unknown"
+		return unknownStr
 	}
 	out, err := runQuickCmd([]string{"uptime"}, 2*time.Second)
 	if err != nil {
-		return "unknown"
+		return unknownStr
 	}
 	line := strings.TrimSpace(out)
 	idx := strings.Index(line, " up ")
 	if idx == -1 {
-		return "unknown"
+		return unknownStr
 	}
 	part := line[idx+4:]
 	if cut := strings.Index(part, "load average"); cut != -1 {
@@ -220,7 +225,7 @@ func firstIfaceLinux(data []byte) string {
 			continue
 		}
 		iface := strings.TrimSpace(parts[0])
-		if iface == "lo" || strings.HasPrefix(iface, "lo") {
+		if iface == loStr || strings.HasPrefix(iface, loStr) {
 			continue
 		}
 		return iface
@@ -248,7 +253,7 @@ func firstIfaceDarwin() string {
 			continue
 		}
 		iface := fields[nIdx]
-		if iface == "lo0" || strings.HasPrefix(iface, "lo") {
+		if iface == lo0Str || strings.HasPrefix(iface, loStr) {
 			continue
 		}
 		return iface
@@ -472,7 +477,7 @@ func sumNetBytesLinux(data []byte) (uint64, bool) {
 			continue
 		}
 		iface := strings.TrimSpace(parts[0])
-		if iface == "lo" || strings.HasPrefix(iface, "lo") {
+		if iface == loStr || strings.HasPrefix(iface, loStr) {
 			continue
 		}
 		fields := strings.Fields(parts[1])
@@ -517,7 +522,7 @@ func sumNetBytesDarwin() (uint64, bool) {
 			continue
 		}
 		iface := fields[nIdx]
-		if iface == "lo0" || strings.HasPrefix(iface, "lo") {
+		if iface == lo0Str || strings.HasPrefix(iface, loStr) {
 			continue
 		}
 		ib, err := strconv.ParseUint(fields[iIdx], 10, 64)

internal/ui/model.go

@@ -36,6 +36,7 @@ type systemMsg struct {
 const (
 	spinnerInterval = 200 * time.Millisecond
 	fixedRows       = 9
+	keyCtrlC        = "ctrl+c"
 )
 
 var spinnerFrames = []string{"|", "/", "-", "\\"}
@@ -89,7 +90,7 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			return m, tea.Quit
 		}
 		switch msg.String() {
-		case "ctrl+c":
+		case keyCtrlC:
 			return m, tea.Quit
 		case "right", "l", "tab":
 			m.active = (m.active + 1) % len(m.tabs)

internal/ui/model_test.go

@@ -21,23 +21,32 @@ func TestModelNavigation(t *testing.T) {
 	// Test moving right
 	msg := tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune{'l'}} // vim binding 'l'
 	newM, _ := m.Update(msg)
-	updatedM := newM.(Model)
+	updatedM, ok := newM.(Model)
+	if !ok {
+		t.Fatal("Expected Model type")
+	}
 
 	if updatedM.active != 1 {
 		t.Errorf("Expected active tab 1, got %d", updatedM.active)
 	}
 
 	// Test moving right again
 	newM, _ = updatedM.Update(msg)
-	updatedM = newM.(Model)
+	updatedM, ok = newM.(Model)
+	if !ok {
+		t.Fatal("Expected Model type")
+	}
 
 	if updatedM.active != 2 {
 		t.Errorf("Expected active tab 2, got %d", updatedM.active)
 	}
 
 	// Test wrapping around
 	newM, _ = updatedM.Update(msg)
-	updatedM = newM.(Model)
+	updatedM, ok = newM.(Model)
+	if !ok {
+		t.Fatal("Expected Model type")
+	}
 
 	if updatedM.active != 0 {
 		t.Errorf("Expected wrap around to 0, got %d", updatedM.active)
@@ -46,7 +55,10 @@ func TestModelNavigation(t *testing.T) {
 	// Test moving left (wrapping back)
 	leftMsg := tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune{'h'}}
 	newM, _ = updatedM.Update(leftMsg)
-	updatedM = newM.(Model)
+	updatedM, ok = newM.(Model)
+	if !ok {
+		t.Fatal("Expected Model type")
+	}
 
 	if updatedM.active != 2 {
 		t.Errorf("Expected wrap back to 2, got %d", updatedM.active)
@@ -59,7 +71,10 @@ func TestThemeToggle(t *testing.T) {
 
 	msg := tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune{'t'}}
 	newM, _ := m.Update(msg)
-	updatedM := newM.(Model)
+	updatedM, ok := newM.(Model)
+	if !ok {
+		t.Fatal("Expected Model type")
+	}
 
 	if updatedM.themeIndex == initialTheme {
 		t.Error("Theme index should change after pressing 't'")