test: add unit tests for RingBuffer in cmd/status

Add comprehensive test coverage for the RingBuffer circular buffer
data structure used in network history tracking.

Test cases:
- Constructor initialization (NewRingBuffer)
- Empty buffer returns nil slice
- Adding elements within capacity
- Exact capacity boundary
- Wrap-around behavior with chronological ordering
- Multiple wrap-arounds stress test
- Single-element buffer edge case
- Slice returns independent copy (not reference)

cmd/status/metrics_test.go

@@ -0,0 +1,160 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestNewRingBuffer(t *testing.T) {
+	tests := []struct {
+		name     string
+		capacity int
+	}{
+		{"small buffer", 5},
+		{"standard buffer", 120},
+		{"single element", 1},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			rb := NewRingBuffer(tt.capacity)
+			if rb == nil {
+				t.Fatal("NewRingBuffer returned nil")
+			}
+			if rb.cap != tt.capacity {
+				t.Errorf("expected capacity %d, got %d", tt.capacity, rb.cap)
+			}
+			if rb.size != 0 {
+				t.Errorf("expected size 0 for new buffer, got %d", rb.size)
+			}
+			if rb.index != 0 {
+				t.Errorf("expected index 0 for new buffer, got %d", rb.index)
+			}
+			if len(rb.data) != tt.capacity {
+				t.Errorf("expected data slice length %d, got %d", tt.capacity, len(rb.data))
+			}
+		})
+	}
+}
+
+func TestRingBuffer_EmptyBuffer(t *testing.T) {
+	rb := NewRingBuffer(5)
+	result := rb.Slice()
+
+	if result != nil {
+		t.Errorf("expected nil for empty buffer, got %v", result)
+	}
+}
+
+func TestRingBuffer_AddWithinCapacity(t *testing.T) {
+	rb := NewRingBuffer(5)
+
+	// Add 3 elements (less than capacity)
+	rb.Add(1.0)
+	rb.Add(2.0)
+	rb.Add(3.0)
+
+	if rb.size != 3 {
+		t.Errorf("expected size 3, got %d", rb.size)
+	}
+
+	result := rb.Slice()
+	expected := []float64{1.0, 2.0, 3.0}
+
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("expected %v, got %v", expected, result)
+	}
+}
+
+func TestRingBuffer_ExactCapacity(t *testing.T) {
+	rb := NewRingBuffer(5)
+
+	// Fill exactly to capacity
+	for i := 1; i <= 5; i++ {
+		rb.Add(float64(i))
+	}
+
+	if rb.size != 5 {
+		t.Errorf("expected size 5, got %d", rb.size)
+	}
+
+	result := rb.Slice()
+	expected := []float64{1.0, 2.0, 3.0, 4.0, 5.0}
+
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("expected %v, got %v", expected, result)
+	}
+}
+
+func TestRingBuffer_WrapAround(t *testing.T) {
+	rb := NewRingBuffer(5)
+
+	// Add 7 elements to trigger wrap-around (2 past capacity)
+	// Internal state after: data=[6, 7, 3, 4, 5], index=2, size=5
+	// Oldest element is at index 2 (value 3)
+	for i := 1; i <= 7; i++ {
+		rb.Add(float64(i))
+	}
+
+	if rb.size != 5 {
+		t.Errorf("expected size to cap at 5, got %d", rb.size)
+	}
+
+	result := rb.Slice()
+	// Should return chronological order: 3, 4, 5, 6, 7
+	expected := []float64{3.0, 4.0, 5.0, 6.0, 7.0}
+
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("expected %v, got %v", expected, result)
+	}
+}
+
+func TestRingBuffer_MultipleWrapArounds(t *testing.T) {
+	rb := NewRingBuffer(3)
+
+	// Add 10 elements (wraps multiple times)
+	for i := 1; i <= 10; i++ {
+		rb.Add(float64(i))
+	}
+
+	result := rb.Slice()
+	// Should have the last 3 values: 8, 9, 10
+	expected := []float64{8.0, 9.0, 10.0}
+
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("expected %v, got %v", expected, result)
+	}
+}
+
+func TestRingBuffer_SingleElementBuffer(t *testing.T) {
+	rb := NewRingBuffer(1)
+
+	rb.Add(5.0)
+	result := rb.Slice()
+	if !reflect.DeepEqual(result, []float64{5.0}) {
+		t.Errorf("expected [5.0], got %v", result)
+	}
+
+	// Overwrite the single element
+	rb.Add(10.0)
+	result = rb.Slice()
+	if !reflect.DeepEqual(result, []float64{10.0}) {
+		t.Errorf("expected [10.0], got %v", result)
+	}
+}
+
+func TestRingBuffer_SliceReturnsNewSlice(t *testing.T) {
+	rb := NewRingBuffer(3)
+	rb.Add(1.0)
+	rb.Add(2.0)
+
+	slice1 := rb.Slice()
+	slice2 := rb.Slice()
+
+	// Modify slice1 and verify slice2 is unaffected
+	slice1[0] = 999.0
+
+	if slice2[0] == 999.0 {
+		t.Error("Slice should return a new copy, not a reference to internal data")
+	}
+}