diff --git a/go.mod b/go.mod
index f35adcb..72812e3 100644
--- a/go.mod
+++ b/go.mod
@@ -1,10 +1,19 @@
 module github.com/mailgun/groupcache/v2
 
+go 1.19
+
 require (
-	github.com/golang/protobuf v1.3.1
+	github.com/golang/protobuf v1.5.2
 	github.com/segmentio/fasthash v1.0.3
-	github.com/sirupsen/logrus v1.6.0
-	golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a // indirect
+	github.com/sirupsen/logrus v1.9.0
+	github.com/stretchr/testify v1.8.1
 )
 
-go 1.15
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	golang.org/x/sys v0.0.0-20220919091848-fb04ddd9f9c8 // indirect
+	golang.org/x/xerrors v0.0.0-20220609144429-65e65417b02f // indirect
+	google.golang.org/protobuf v1.28.1 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
diff --git a/go.sum b/go.sum
index e6f4bb4..e1d0665 100644
--- a/go.sum
+++ b/go.sum
@@ -1,18 +1,37 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/golang/protobuf v1.3.1 h1:YF8+flBXS5eO826T4nzqPrxfhQThhXl0YzfuUPu4SBg=
-github.com/golang/protobuf v1.3.1/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
-github.com/konsorten/go-windows-terminal-sequences v1.0.3 h1:CE8S1cTafDpPvMhIxNJKvHsGVBgn1xWYf1NbHQhywc8=
-github.com/konsorten/go-windows-terminal-sequences v1.0.3/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
+github.com/golang/protobuf v1.5.2 h1:ROPKBNFfQgOUMifHyP+KYbvpjbdoFNs+aK7DXlji0Tw=
+github.com/golang/protobuf v1.5.2/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
+github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/segmentio/fasthash v1.0.3 h1:EI9+KE1EwvMLBWwjpRDc+fEM+prwxDYbslddQGtrmhM=
 github.com/segmentio/fasthash v1.0.3/go.mod h1:waKX8l2N8yckOgmSsXJi7x1ZfdKZ4x7KRMzBtS3oedY=
-github.com/sirupsen/logrus v1.6.0 h1:UBcNElsrwanuuMsnGSlYmtmgbb23qDR5dG+6X6Oo89I=
-github.com/sirupsen/logrus v1.6.0/go.mod h1:7uNnSEd1DgxDLC74fIahvMZmmYsHGZGEOFrfsX/uA88=
-github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
-github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
-golang.org/x/sys v0.0.0-20190422165155-953cdadca894 h1:Cz4ceDQGXuKRnVBDTS23GTn/pU5OE2C0WrNTOYK1Uuc=
-golang.org/x/sys v0.0.0-20190422165155-953cdadca894/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a h1:dGzPydgVsqGcTRVwiLJ1jVbufYwmzD3LfVPLKsKg+0k=
-golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=
+github.com/sirupsen/logrus v1.9.0/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
+github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
+golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220919091848-fb04ddd9f9c8 h1:h+EGohizhe9XlX18rfpa8k8RAc5XyaeamM+0VHRd4lc=
+golang.org/x/sys v0.0.0-20220919091848-fb04ddd9f9c8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20220609144429-65e65417b02f h1:uF6paiQQebLeSXkrTqHqz0MXhXXS1KgF41eUdBNvxK0=
+golang.org/x/xerrors v0.0.0-20220609144429-65e65417b02f/go.mod h1:K8+ghG5WaK9qNqU5K3HdILfMLy1f3aNYFI/wnl100a8=
+google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
+google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
+google.golang.org/protobuf v1.28.1 h1:d0NfwRgPtno5B1Wa6L2DAG+KivqkdutMf1UhdNx175w=
+google.golang.org/protobuf v1.28.1/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/groupcache.go b/groupcache.go
index 1eff499..3d1ebec 100644
--- a/groupcache.go
+++ b/groupcache.go
@@ -582,6 +582,11 @@ func (g *Group) CacheStats(which CacheType) CacheStats {
 	}
 }
 
+// NowFunc returns the current time which is used by the LRU to
+// determine if the value has expired. This can be overridden by
+// tests to ensure items are evicted when expired.
+var NowFunc lru.NowFunc = time.Now
+
 // cache is a wrapper around an *lru.Cache that adds synchronization,
 // makes values always be ByteView, and counts the size of all keys and
 // values.
@@ -610,6 +615,7 @@ func (c *cache) add(key string, value ByteView) {
 	defer c.mu.Unlock()
 	if c.lru == nil {
 		c.lru = &lru.Cache{
+			Now: NowFunc,
 			OnEvicted: func(key lru.Key, value interface{}) {
 				val := value.(ByteView)
 				c.nbytes -= int64(len(key.(string))) + int64(val.Len())
diff --git a/groupcache_test.go b/groupcache_test.go
index 5eca5e2..4a667ed 100644
--- a/groupcache_test.go
+++ b/groupcache_test.go
@@ -30,9 +30,9 @@ import (
 	"unsafe"
 
 	"github.com/golang/protobuf/proto"
-
 	pb "github.com/mailgun/groupcache/v2/groupcachepb"
 	"github.com/mailgun/groupcache/v2/testpb"
+	"github.com/stretchr/testify/assert"
 )
 
 var (
@@ -536,17 +536,105 @@ func TestContextDeadlineOnPeer(t *testing.T) {
 	}
 }
 
-func TestCacheRemovesBytesOfReplacedValues(t *testing.T) {
-	c := cache{}
+func TestEnsureSizeReportedCorrectly(t *testing.T) {
+	c := &cache{}
 
-	const key = "test"
-	keyLen := len(key)
+	// Add the first value
+	bv1 := ByteView{s: "first", e: time.Now().Add(100 * time.Second)}
+	c.add("key1", bv1)
+	v, ok := c.get("key1")
 
-	for _, bytes := range []int{100, 1000, 2000} {
-		c.add(key, ByteView{b: make([]byte, bytes)})
-		expected := int64(bytes + keyLen)
-		if c.nbytes != expected {
-			t.Fatalf("%s: expected %d was %d", t.Name(), expected, c.nbytes)
-		}
+	// Should be len("key1" + "first") == 9
+	assert.True(t, ok)
+	assert.True(t, v.Equal(bv1))
+	assert.Equal(t, int64(9), c.bytes())
+
+	// Add a second value
+	bv2 := ByteView{s: "second", e: time.Now().Add(200 * time.Second)}
+
+	c.add("key2", bv2)
+	v, ok = c.get("key2")
+
+	// Should be len("key2" + "second") == (10 + 9) == 19
+	assert.True(t, ok)
+	assert.True(t, v.Equal(bv2))
+	assert.Equal(t, int64(19), c.bytes())
+
+	// Replace the first value with a shorter value
+	bv3 := ByteView{s: "3", e: time.Now().Add(200 * time.Second)}
+
+	c.add("key1", bv3)
+	v, ok = c.get("key1")
+
+	// len("key1" + "3") == 5
+	// len("key2" + "second") == 10
+	assert.True(t, ok)
+	assert.True(t, v.Equal(bv3))
+	assert.Equal(t, int64(15), c.bytes())
+
+	// Replace the second value with a longer value
+	bv4 := ByteView{s: "this-string-is-28-chars-long", e: time.Now().Add(200 * time.Second)}
+
+	c.add("key2", bv4)
+	v, ok = c.get("key2")
+
+	// len("key1" + "3") == 5
+	// len("key2" + "this-string-is-28-chars-long") == 32
+	assert.True(t, ok)
+	assert.True(t, v.Equal(bv4))
+	assert.Equal(t, int64(37), c.bytes())
+}
+
+func TestEnsureUpdateExpiredValue(t *testing.T) {
+	c := &cache{}
+	curTime := time.Now()
+
+	// Override the now function so we control time
+	NowFunc = func() time.Time {
+		return curTime
 	}
+
+	// Expires in 1 second
+	c.add("key1", ByteView{s: "value1", e: curTime.Add(time.Second)})
+	_, ok := c.get("key1")
+	assert.True(t, ok)
+
+	// Advance 1.1 seconds into the future
+	curTime = curTime.Add(time.Millisecond * 1100)
+
+	// Value should have expired
+	_, ok = c.get("key1")
+	assert.False(t, ok)
+
+	// Add a new key that expires in 1 second
+	c.add("key2", ByteView{s: "value2", e: curTime.Add(time.Second)})
+	_, ok = c.get("key2")
+	assert.True(t, ok)
+
+	// Advance 0.5 seconds into the future
+	curTime = curTime.Add(time.Millisecond * 500)
+
+	// Value should still exist
+	_, ok = c.get("key2")
+	assert.True(t, ok)
+
+	// Replace the existing key, this should update the expired time
+	c.add("key2", ByteView{s: "updated value2", e: curTime.Add(time.Second)})
+	_, ok = c.get("key2")
+	assert.True(t, ok)
+
+	// Advance 0.6 seconds into the future, which puts us past the initial
+	// expired time for key2.
+	curTime = curTime.Add(time.Millisecond * 600)
+
+	// Should still exist
+	_, ok = c.get("key2")
+	assert.True(t, ok)
+
+	// Advance 1.1 seconds into the future
+	curTime = curTime.Add(time.Millisecond * 1100)
+
+	// Should not exist
+	_, ok = c.get("key2")
+	assert.False(t, ok)
 }
diff --git a/lru/lru.go b/lru/lru.go
index 549122f..e278234 100644
--- a/lru/lru.go
+++ b/lru/lru.go
@@ -22,6 +22,8 @@ import (
 	"time"
 )
 
+type NowFunc func() time.Time
+
 // Cache is an LRU cache. It is not safe for concurrent access.
 type Cache struct {
 	// MaxEntries is the maximum number of cache entries before
@@ -32,6 +34,11 @@ type Cache struct {
 	// executed when an entry is purged from the cache.
 	OnEvicted func(key Key, value interface{})
 
+	// Now is the Now() function the cache will use to determine
+	// the current time which is used to calculate expired values
+	// Defaults to time.Now()
+	Now NowFunc
+
 	ll    *list.List
 	cache map[interface{}]*list.Element
 }
@@ -53,6 +60,7 @@ func New(maxEntries int) *Cache {
 		MaxEntries: maxEntries,
 		ll:         list.New(),
 		cache:      make(map[interface{}]*list.Element),
+		Now:        time.Now,
 	}
 }
 
@@ -68,6 +76,7 @@ func (c *Cache) Add(key Key, value interface{}, expire time.Time) {
 			c.OnEvicted(key, eee.value)
 		}
 		c.ll.MoveToFront(ee)
+		eee.expire = expire
 		eee.value = value
 		return
 	}
@@ -86,7 +95,7 @@ func (c *Cache) Get(key Key) (value interface{}, ok bool) {
 	if ele, hit := c.cache[key]; hit {
 		entry := ele.Value.(*entry)
 		// If the entry has expired, remove it from the cache
-		if !entry.expire.IsZero() && entry.expire.Before(time.Now()) {
+		if !entry.expire.IsZero() && entry.expire.Before(c.Now()) {
 			c.removeElement(ele)
 			return nil, false
 		}