diff --git a/mocks/sr.lua b/mocks/sr.lua
index a7a667f..a513ec7 100644
--- a/mocks/sr.lua
+++ b/mocks/sr.lua
@@ -491,6 +491,7 @@ xavpMock = {
         end
 
         function t.get(xavp_name, index, mode)
+            if not mode then mode = 0 end
             xavp = t._get_xavp(xavp_name, index, mode)
             return xavp
         end
diff --git a/tests/ngcp.lua b/tests/ngcp.lua
index 69f5dfc..ab2cc0d 100644
--- a/tests/ngcp.lua
+++ b/tests/ngcp.lua
@@ -375,7 +375,7 @@ TestNGCP = {} --class
     end
 
     function TestNGCP:test_tostring()
-        assertEquals(tostring(self.ngcp), 'caller_contract_prefs:{dummy="caller"}\ncallee_contract_prefs:{dummy="callee"}\ncaller_peer_prefs:{dummy="caller"}\ncallee_peer_prefs:{dummy="callee"}\ncaller_dom_prefs:{dummy="caller"}\ncallee_dom_prefs:{dummy="callee"}\ncaller_usr_prefs:{dummy="caller"}\ncallee_usr_prefs:{dummy="callee"}\ncaller_real_prefs:{dummy="caller"}\ncallee_real_prefs:{dummy="callee"}\n')
+        assertEquals(tostring(self.ngcp), 'caller_contract_prefs:{dummy={"caller"}}\ncallee_contract_prefs:{dummy={"callee"}}\ncaller_peer_prefs:{dummy={"caller"}}\ncallee_peer_prefs:{dummy={"callee"}}\ncaller_dom_prefs:{dummy={"caller"}}\ncallee_dom_prefs:{dummy={"callee"}}\ncaller_usr_prefs:{dummy={"caller"}}\ncallee_usr_prefs:{dummy={"callee"}}\ncaller_real_prefs:{dummy={"caller"}}\ncallee_real_prefs:{dummy={"callee"}}\n')
     end
 -- class TestNGCP
 --EOF
diff --git a/tests/ngcp_dp.lua b/tests/ngcp_dp.lua
index fc8cbbe..1a86a53 100644
--- a/tests/ngcp_dp.lua
+++ b/tests/ngcp_dp.lua
@@ -194,7 +194,7 @@ TestNGCPDomainPrefs = {} --class
         local caller_xavp = NGCPDomainPrefs:xavp('caller')
         caller_xavp("other",1)
         caller_xavp("otherfoo","foo")
-        assertEquals(tostring(self.d), 'caller_dom_prefs:{other=1,otherfoo="foo",dummy="caller"}\ncallee_dom_prefs:{dummy="callee",testid=1,foo="foo"}\n')
+        assertEquals(tostring(self.d), 'caller_dom_prefs:{other={1},otherfoo={"foo"},dummy={"caller"}}\ncallee_dom_prefs:{dummy={"callee"},testid={1},foo={"foo"}}\n')
     end
 -- class TestNGCPDomainPrefs
 --EOF
\ No newline at end of file
diff --git a/tests/ngcp_pp.lua b/tests/ngcp_pp.lua
index 269d3bf..7141375 100644
--- a/tests/ngcp_pp.lua
+++ b/tests/ngcp_pp.lua
@@ -209,7 +209,7 @@ TestNGCPPeerPrefs = {} --class
         local caller_xavp = NGCPPeerPrefs:xavp('caller')
         caller_xavp("other",1)
         caller_xavp("otherfoo","foo")
-        assertEquals(tostring(self.d), 'caller_peer_prefs:{other=1,otherfoo="foo",dummy="caller"}\ncallee_peer_prefs:{dummy="callee",testid=1,foo="foo"}\n')
+        assertEquals(tostring(self.d), 'caller_peer_prefs:{other={1},otherfoo={"foo"},dummy={"caller"}}\ncallee_peer_prefs:{dummy={"callee"},testid={1},foo={"foo"}}\n')
     end
 -- class TestNGCPPeerPrefs
 --EOF
\ No newline at end of file
diff --git a/tests/ngcp_rp.lua b/tests/ngcp_rp.lua
index 0080d54..dbcc20f 100644
--- a/tests/ngcp_rp.lua
+++ b/tests/ngcp_rp.lua
@@ -260,7 +260,7 @@ TestNGCPRealPrefs = {} --class
         callee_xavp("foo","foo")
         caller_xavp("other",1)
         caller_xavp("otherfoo","foo")
-        assertEquals(tostring(self.real),'caller_real_prefs:{other=1,otherfoo="foo",dummy="caller"}\ncallee_real_prefs:{dummy="callee",testid=1,foo="foo"}\n')
+        assertEquals(tostring(self.real),'caller_real_prefs:{other={1},otherfoo={"foo"},dummy={"caller"}}\ncallee_real_prefs:{dummy={"callee"},testid={1},foo={"foo"}}\n')
     end
 -- class TestNGCPRealPrefs
 --EOF
\ No newline at end of file
diff --git a/tests/ngcp_up.lua b/tests/ngcp_up.lua
index ed053bd..a425bee 100644
--- a/tests/ngcp_up.lua
+++ b/tests/ngcp_up.lua
@@ -213,7 +213,7 @@ TestNGCPUserPrefs = {} --class
         local caller_xavp = NGCPUserPrefs:xavp('caller')
         caller_xavp("other",1)
         caller_xavp("otherfoo","foo")
-        assertEquals(tostring(self.d),'caller_usr_prefs:{other=1,otherfoo="foo",dummy="caller"}\ncallee_usr_prefs:{dummy="callee",testid=1,foo="foo"}\n')
+        assertEquals(tostring(self.d), 'caller_usr_prefs:{other={1},otherfoo={"foo"},dummy={"caller"}}\ncallee_usr_prefs:{dummy={"callee"},testid={1},foo={"foo"}}\n')
     end
 -- class TestNGCPUserPrefs
 --EOF
\ No newline at end of file
diff --git a/tests/ngcp_xavp.lua b/tests/ngcp_xavp.lua
index 957336a..e762090 100644
--- a/tests/ngcp_xavp.lua
+++ b/tests/ngcp_xavp.lua
@@ -135,7 +135,7 @@ TestNGCPXAvp = {} --class
 
     function TestNGCPXAvp:test_tostring()
         local xavp = NGCPXAvp:new("caller", "peer", {})
-        assertEquals(tostring(xavp), '{dummy="caller"}')
+        assertEquals(tostring(xavp), '{dummy={"caller"}}')
     end
 
     function TestNGCPXAvp:test_keys()