Added tests for LRU cache (#1388)

What changed?
Added tests for the LRU cache in client

The tests checks the current behaviour. The current behaviour should work but especially the pin API seems very fragile.

Why?
Improve test coverage

How did you test it?

Potential risks

internal/common/cache/lru_test.go

@@ -26,6 +26,7 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestLRU(t *testing.T) {
@@ -62,6 +63,79 @@ func TestLRU(t *testing.T) {
 	assert.Nil(t, cache.Get("A"))
 }
 
+func TestExist(t *testing.T) {
+	cache := NewLRUWithInitialCapacity(5, 5)
+
+	assert.False(t, cache.Exist("A"))
+
+	cache.Put("A", "Foo")
+	assert.True(t, cache.Exist("A"))
+	assert.False(t, cache.Exist("B"))
+
+	cache.Put("B", "Bar")
+	assert.True(t, cache.Exist("B"))
+
+	cache.Delete("A")
+	assert.False(t, cache.Exist("A"))
+}
+
+func TestPutIfNotExistSuccess(t *testing.T) {
+	cache := New(2, nil)
+
+	existing, err := cache.PutIfNotExist("A", "Foo")
+	assert.NoError(t, err)
+	assert.Equal(t, "Foo", existing)
+
+	existing, err = cache.PutIfNotExist("A", "Bar")
+	assert.NoError(t, err)
+	assert.Equal(t, "Foo", existing)
+
+	assert.Equal(t, "Foo", cache.Get("A"))
+}
+
+func TestNoPutInPin(t *testing.T) {
+	cache := New(2, &Options{
+		Pin: true,
+	})
+
+	assert.Panics(t, func() {
+		cache.Put("A", "Foo")
+	})
+}
+
+func TestPinningTTL(t *testing.T) {
+	cache := New(3, &Options{
+		Pin: true,
+		TTL: time.Millisecond * 100,
+	}).(*lru)
+
+	currentTime := time.UnixMilli(123)
+	cache.now = func() time.Time { return currentTime }
+
+	// Add two elements so the cache is full
+	_, err := cache.PutIfNotExist("A", "Foo")
+	require.NoError(t, err)
+	_, err = cache.PutIfNotExist("B", "Bar")
+	require.NoError(t, err)
+
+	// Release B so it can be evicted
+	cache.Release("B")
+
+	currentTime = currentTime.Add(time.Millisecond * 300)
+	assert.Equal(t, "Foo", cache.Get("A"))
+
+	// B can be evicted, so we can add another element
+	_, err = cache.PutIfNotExist("C", "Baz")
+	require.NoError(t, err)
+
+	// A cannot be evicted since it's pinned, so we can't add another element
+	_, err = cache.PutIfNotExist("D", "Qux")
+	assert.ErrorContains(t, err, "Cache capacity is fully occupied with pinned elements")
+
+	// B is gone
+	assert.Nil(t, cache.Get("B"))
+}
+
 func TestLRUWithTTL(t *testing.T) {
 	cache := New(5, &Options{
 		TTL: time.Millisecond * 100,