diff --git a/heap/heap.go b/heap/heap.go
index eeb1fbb..673853e 100644
--- a/heap/heap.go
+++ b/heap/heap.go
@@ -22,7 +22,7 @@ type Min struct {
 func NewMin(k int) *Min {
 	return &Min{
 		K:     k,
-		Items: make([]Item, k),
+		Items: make([]Item, 0, k),
 		Index: make(map[string]int, k),
 	}
 }
@@ -31,7 +31,7 @@ var _ heap.Interface = &Min{}
 
 func (me Min) SizeBytes() int {
 	structSize := sizeofMinStruct
-	bucketsSize := len(me.Items)*sizeofItem + me.StoredKeysBytes
+	bucketsSize := cap(me.Items)*sizeofItem + me.StoredKeysBytes
 	indexSize := sizeof.StringIntMap + (sizeof.Int+sizeof.String)*len(me.Index)
 	return structSize + bucketsSize + indexSize
 }
@@ -127,7 +127,7 @@ func (me *Min) Update(item string, fingerprint uint32, count uint32) bool {
 	me.StoredKeysBytes += len(item)
 
 	if !me.Full() { // heap not full: add to heap
-		me.Push(Item{
+		heap.Push(me, Item{
 			Count:       count,
 			Fingerprint: fingerprint,
 			Item:        item,
diff --git a/heap/heap_test.go b/heap/heap_test.go
new file mode 100644
index 0000000..fb669d6
--- /dev/null
+++ b/heap/heap_test.go
@@ -0,0 +1,180 @@
+package heap_test
+
+import (
+	"testing"
+	"unsafe"
+
+	"github.com/keilerkonzept/topk/heap"
+	sketchheap "github.com/keilerkonzept/topk/heap"
+	"github.com/keilerkonzept/topk/internal/sizeof"
+)
+
+func TestMinHeap_LessSwap(t *testing.T) {
+	h := sketchheap.NewMin(5)
+
+	h.Items = []sketchheap.Item{
+		{Item: "a", Count: 5, Fingerprint: 1},
+		{Item: "b", Count: 2, Fingerprint: 2},
+		{Item: "c", Count: 3, Fingerprint: 3},
+	}
+
+	// Check Less function
+	if !h.Less(1, 0) {
+		t.Errorf("expected Less(1, 0) to be true")
+	}
+	if h.Less(0, 1) {
+		t.Errorf("expected Less(0, 1) to be false")
+	}
+
+	// Check Swap function
+	h.Swap(0, 1)
+	if h.Items[0].Item != "b" || h.Items[1].Item != "a" {
+		t.Errorf("expected Swap to switch elements 'a' and 'b'")
+	}
+}
+
+func TestMinHeap_Full(t *testing.T) {
+	h := sketchheap.NewMin(2)
+
+	h.Update("a", 1, 2)
+	if h.Full() {
+		t.Errorf("expected heap to not be full")
+	}
+
+	h.Update("b", 2, 2)
+	if !h.Full() {
+		t.Errorf("expected heap to be full")
+	}
+}
+
+func TestMinHeap_Update(t *testing.T) {
+	h := sketchheap.NewMin(2)
+
+	// Insert new item
+	h.Update("a", 1, 10)
+	if h.Items[0].Item != "a" {
+		t.Errorf("expected 'a' to be in the heap")
+	}
+
+	// Insert more items
+	h.Update("b", 2, 5)
+	h.Update("c", 3, 8)
+	h.Update("d", 3, 1)
+
+	// "b" should be removed as it has the lowest count and heap is full
+	if h.Contains("b") {
+		t.Errorf("expected 'b' to be removed from the heap")
+	}
+	// "d" should be not enter the heap as its below the Min()
+	if h.Contains("d") {
+		t.Errorf("expected 'd' to never enter the heap")
+	}
+
+	// Update an existing item
+	h.Update("c", 3, 15)
+	if h.Items[0].Item != "a" || h.Items[1].Item != "c" {
+		t.Errorf("expected 'a' and 'c' to be in the heap after update")
+	}
+}
+
+func TestMinHeap_Min(t *testing.T) {
+	h := sketchheap.NewMin(2)
+
+	// Empty heap
+	if h.Min() != 0 {
+		t.Errorf("expected Min to return 0 for empty heap")
+	}
+
+	// Push some items and check minimum
+	h.Update("a", 1, 10)
+	h.Update("b", 2, 5)
+	h.Update("c", 2, 3)
+
+	if h.Min() != 5 {
+		t.Errorf("expected Min to return 5, got %d", h.Min())
+	}
+}
+
+func TestMinHeap_Reinit(t *testing.T) {
+	h := sketchheap.NewMin(3)
+
+	h.Push(sketchheap.Item{Item: "a", Count: 0, Fingerprint: 1})
+	h.Push(sketchheap.Item{Item: "b", Count: 2, Fingerprint: 2})
+	h.Push(sketchheap.Item{Item: "c", Count: 3, Fingerprint: 3})
+
+	// Reinit should remove items with 0 count
+	h.Reinit()
+	if h.Len() != 2 {
+		t.Errorf("expected Len after Reinit to be 2, got %d", h.Len())
+	}
+	if h.Contains("a") {
+		t.Errorf("expected 'a' to be removed from the heap")
+	}
+}
+
+func TestMinHeap_Find(t *testing.T) {
+	h := sketchheap.NewMin(3)
+	h.Update("a", 1, 10)
+
+	// Find existing item
+	idx := h.Find("a")
+	if idx != 0 {
+		t.Errorf("expected 'a' to be at index 0, got %d", idx)
+	}
+
+	// Find non-existing item
+	idx = h.Find("b")
+	if idx != -1 {
+		t.Errorf("expected 'b' to not be found, got %d", idx)
+	}
+}
+
+func TestMinHeap_Get(t *testing.T) {
+	h := sketchheap.NewMin(3)
+	h.Update("a", 1, 10)
+
+	// Get existing item
+	item := h.Get("a")
+	if item == nil || item.Item != "a" {
+		t.Errorf("expected to get item 'a', got '%v'", item)
+	}
+
+	// Get non-existing item
+	item = h.Get("b")
+	if item != nil {
+		t.Errorf("expected to get nil for non-existing item, got '%v'", item)
+	}
+}
+
+func TestMinHeap_SizeBytes(t *testing.T) {
+	h := heap.NewMin(3)
+
+	const (
+		sizeofMinStruct = int(unsafe.Sizeof(sketchheap.Min{}))
+		sizeofItem      = int(unsafe.Sizeof(sketchheap.Item{}))
+	)
+
+	// Initial size should only account for the struct and empty containers
+	expectedSize := sizeofMinStruct + 3*sizeofItem + sizeof.StringIntMap
+	if h.SizeBytes() != expectedSize {
+		t.Errorf("expected SizeBytes to be %d, got %d", expectedSize, h.SizeBytes())
+	}
+
+	h.Update("a", 1, 5)
+	expectedSize += len("a") + sizeof.String + sizeof.Int // Size of new item in heap
+	if h.SizeBytes() != expectedSize {
+		t.Errorf("expected SizeBytes to be %d, got %d", expectedSize, h.SizeBytes())
+	}
+
+	h.Update("b", 2, 10)
+	expectedSize += len("b") + sizeof.String + sizeof.Int
+	if h.SizeBytes() != expectedSize {
+		t.Errorf("expected SizeBytes to be %d, got %d", expectedSize, h.SizeBytes())
+	}
+
+	h.Update("long_string_item", 3, 15)
+	expectedSize += len("long_string_item") + sizeof.String + sizeof.Int
+	if h.SizeBytes() != expectedSize {
+		t.Errorf("expected SizeBytes to be %d, got %d", expectedSize, h.SizeBytes())
+	}
+}