Added the subPrefixDb mock

internal/mocks/subprefixdbmock.go

@@ -0,0 +1,21 @@
+package mocks
+
+import (
+	"context"
+
+	"github.com/stretchr/testify/mock"
+)
+
+type MockSubPrefixDb struct {
+	mock.Mock
+}
+
+func (m *MockSubPrefixDb) Get(ctx context.Context, key []byte) ([]byte, error) {
+	args := m.Called(ctx, key)
+	return args.Get(0).([]byte), args.Error(1)
+}
+
+func (m *MockSubPrefixDb) Put(ctx context.Context, key, val []byte) error {
+	args := m.Called(ctx, key, val)
+	return args.Error(0)
+}