tests: add test for queue implementation

internal/queue/queue_test.go

@@ -1 +1,87 @@
 package queue_test
+
+import (
+	"testing"
+
+	"github.com/StevanFreeborn/advent-of-code-2025/internal/queue"
+)
+
+func TestQueue_EnqueueDequeue(t *testing.T) {
+	q := queue.New[int]()
+
+	q.Enqueue(1)
+	q.Enqueue(2)
+	q.Enqueue(3)
+
+	expectedValues := []int{1, 2, 3}
+
+	for _, expected := range expectedValues {
+		value, ok := q.Dequeue()
+
+		if !ok {
+			t.Errorf("expected dequeue to be successful, but it failed")
+		}
+
+		if value != expected {
+			t.Errorf("expected value to be %d, got %d", expected, value)
+		}
+
+	}
+
+	_, ok := q.Dequeue()
+
+	if ok {
+		t.Errorf("expected dequeue to fail on empty queue, but it succeeded")
+	}
+
+	if !q.IsEmpty() {
+		t.Errorf("expected queue to be empty, but it is not")
+	}
+}
+
+func TestQueue_Size(t *testing.T) {
+	q := queue.New[string]()
+
+	if q.Size() != 0 {
+		t.Errorf("expected size to be 0, got %d", q.Size())
+	}
+
+	q.Enqueue("a")
+	q.Enqueue("b")
+
+	if q.Size() != 2 {
+		t.Errorf("expected size to be 2, got %d", q.Size())
+	}
+
+	q.Dequeue()
+
+	if q.Size() != 1 {
+		t.Errorf("expected size to be 1, got %d", q.Size())
+	}
+}
+
+func TestQueue_ConcurrentAccess(t *testing.T) {
+	q := queue.New[int]()
+	done := make(chan bool)
+	numGoroutines := 100
+	numItemsPerGoroutine := 100
+
+	for i := range numGoroutines {
+		go func(start int) {
+			for j := range numItemsPerGoroutine {
+				q.Enqueue(start + j)
+			}
+			done <- true
+		}(i * numItemsPerGoroutine)
+	}
+
+	for range numGoroutines {
+		<-done
+	}
+
+	expectedSize := numGoroutines * numItemsPerGoroutine
+
+	if q.Size() != expectedSize {
+		t.Errorf("expected size to be %d, got %d", expectedSize, q.Size())
+	}
+}