diff --git a/test/unit/api/test_sockets.c b/test/unit/api/test_sockets.c
index a4362142..4972f28a 100644
--- a/test/unit/api/test_sockets.c
+++ b/test/unit/api/test_sockets.c
@@ -7,6 +7,7 @@
 #include "lwip/stats.h"
 
 #include "lwip/tcpip.h"
+#include "lwip/priv/tcp_priv.h"
 
 
 static int
@@ -32,12 +33,23 @@ test_sockets_get_used_count(void)
 static void
 sockets_setup(void)
 {
+  /* expect full free heap */
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void
 sockets_teardown(void)
 {
   fail_unless(test_sockets_get_used_count() == 0);
+  /* poll until all memory is released... */
+  tcpip_thread_poll_one();
+  while (tcp_tw_pcbs) {
+    tcp_abort(tcp_tw_pcbs);
+    tcpip_thread_poll_one();
+  }
+  tcpip_thread_poll_one();
+  /* ensure full free heap */
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 #ifndef NUM_SOCKETS
diff --git a/test/unit/core/test_mem.c b/test/unit/core/test_mem.c
index 66b4877e..c362758d 100644
--- a/test/unit/core/test_mem.c
+++ b/test/unit/core/test_mem.c
@@ -15,11 +15,13 @@
 static void
 mem_setup(void)
 {
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void
 mem_teardown(void)
 {
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 
diff --git a/test/unit/core/test_pbuf.c b/test/unit/core/test_pbuf.c
index 8ce0e9d3..86b90b29 100644
--- a/test/unit/core/test_pbuf.c
+++ b/test/unit/core/test_pbuf.c
@@ -18,11 +18,13 @@
 static void
 pbuf_setup(void)
 {
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void
 pbuf_teardown(void)
 {
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 
diff --git a/test/unit/dhcp/test_dhcp.c b/test/unit/dhcp/test_dhcp.c
index 47aaa084..1b0c8843 100644
--- a/test/unit/dhcp/test_dhcp.c
+++ b/test/unit/dhcp/test_dhcp.c
@@ -121,7 +121,8 @@ static enum tcase {
   TEST_LWIP_DHCP_NAK,
   TEST_LWIP_DHCP_RELAY,
   TEST_LWIP_DHCP_NAK_NO_ENDMARKER,
-  TEST_LWIP_DHCP_INVALID_OVERLOAD
+  TEST_LWIP_DHCP_INVALID_OVERLOAD,
+  TEST_NONE
 } tcase;
 
 static int debug = 0;
@@ -188,10 +189,12 @@ static err_t testif_init(struct netif *netif)
 static void dhcp_setup(void)
 {
   txpacket = 0;
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void dhcp_teardown(void)
 {
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void check_pkt(struct pbuf *p, u32_t pos, const u8_t *mem, u32_t len)
@@ -490,6 +493,9 @@ START_TEST(test_dhcp)
   fail_if(memcmp(&netmask, &net_test.netmask, sizeof(ip4_addr_t)));
   fail_if(memcmp(&gw, &net_test.gw, sizeof(ip4_addr_t)));
 
+  tcase = TEST_NONE;
+  dhcp_stop(&net_test);
+  dhcp_cleanup(&net_test);
   netif_remove(&net_test);
 }
 END_TEST
@@ -552,6 +558,9 @@ START_TEST(test_dhcp_nak)
 
   fail_unless(txpacket == 4); /* DHCP nak sent */
 
+  tcase = TEST_NONE;
+  dhcp_stop(&net_test);
+  dhcp_cleanup(&net_test);
   netif_remove(&net_test);
 }
 END_TEST
@@ -796,6 +805,9 @@ START_TEST(test_dhcp_relayed)
 
   fail_unless(txpacket == 7, "txpacket = %d", txpacket);
 
+  tcase = TEST_NONE;
+  dhcp_stop(&net_test);
+  dhcp_cleanup(&net_test);
   netif_remove(&net_test);
 
 }
@@ -899,6 +911,9 @@ START_TEST(test_dhcp_nak_no_endmarker)
   /* NAK should put us in another state for a while, no other way detecting it */
   fail_unless(netif_dhcp_data(&net_test)->state != DHCP_STATE_REQUESTING);
 
+  tcase = TEST_NONE;
+  dhcp_stop(&net_test);
+  dhcp_cleanup(&net_test);
   netif_remove(&net_test);
 }
 END_TEST
@@ -1005,6 +1020,9 @@ START_TEST(test_dhcp_invalid_overload)
   fail_unless(txpacket == 2); /* No more sent */
   xid = htonl(netif_dhcp_data(&net_test)->xid); /* xid updated */
 
+  tcase = TEST_NONE;
+  dhcp_stop(&net_test);
+  dhcp_cleanup(&net_test);
   netif_remove(&net_test);
 }
 END_TEST
diff --git a/test/unit/etharp/test_etharp.c b/test/unit/etharp/test_etharp.c
index 59d73b9b..67b02d0b 100644
--- a/test/unit/etharp/test_etharp.c
+++ b/test/unit/etharp/test_etharp.c
@@ -119,6 +119,7 @@ etharp_setup(void)
 {
   etharp_remove_all();
   default_netif_add();
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void
@@ -126,6 +127,7 @@ etharp_teardown(void)
 {
   etharp_remove_all();
   default_netif_remove();
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 
diff --git a/test/unit/ip4/test_ip4.c b/test/unit/ip4/test_ip4.c
index e0e82d8d..a5a7fd93 100644
--- a/test/unit/ip4/test_ip4.c
+++ b/test/unit/ip4/test_ip4.c
@@ -6,6 +6,8 @@
 #include "lwip/prot/ip.h"
 #include "lwip/prot/ip4.h"
 
+#include "lwip/tcpip.h"
+
 #if !LWIP_IPV4 || !IP_REASSEMBLY || !MIB2_STATS || !IPFRAG_STATS
 #error "This tests needs LWIP_IPV4, IP_REASSEMBLY; MIB2- and IPFRAG-statistics enabled"
 #endif
@@ -55,6 +57,7 @@ create_ip4_input_fragment(u16_t ip_id, u16_t start, u16_t len, int last)
 static void
 ip4_setup(void)
 {
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void
@@ -65,6 +68,9 @@ ip4_teardown(void)
     netif_list->loop_first = NULL;
   }
   netif_list->loop_last = NULL;
+  /* poll until all memory is released... */
+  tcpip_thread_poll_one();
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 
diff --git a/test/unit/lwip_check.h b/test/unit/lwip_check.h
index 0c218d1d..73468ddf 100644
--- a/test/unit/lwip_check.h
+++ b/test/unit/lwip_check.h
@@ -34,4 +34,9 @@ Suite* create_suite(const char* name, testfunc *tests, size_t num_tests, SFun se
 int lwip_unittests_run(void)
 #endif
 
+/* helper functions */
+#define SKIP_POOL(x) (1 << x)
+#define SKIP_HEAP    (1 << MEMP_MAX)
+void lwip_check_ensure_no_alloc(uint32_t skip);
+
 #endif /* LWIP_HDR_LWIP_CHECK_H */
diff --git a/test/unit/lwip_unittests.c b/test/unit/lwip_unittests.c
index dd53a204..f0dce30d 100644
--- a/test/unit/lwip_unittests.c
+++ b/test/unit/lwip_unittests.c
@@ -33,6 +33,23 @@ Suite* create_suite(const char* name, testfunc *tests, size_t num_tests, SFun se
   return s;
 }
 
+void lwip_check_ensure_no_alloc(uint32_t skip)
+{
+  int i;
+  uint32_t mask;
+
+  fail_unless(skip != 0);
+
+  if (!(skip & SKIP_HEAP)) {
+    fail_unless(lwip_stats.mem.used == 0);
+  }
+  for (i = 0, mask = 1; i < MEMP_MAX; i++, mask <<= 1) {
+    if (!(skip & mask)) {
+      fail_unless(lwip_stats.memp[i]->used == 0);
+    }
+  }
+}
+
 #ifdef LWIP_UNITTESTS_LIB
 int lwip_unittests_run(void)
 #else
diff --git a/test/unit/mqtt/test_mqtt.c b/test/unit/mqtt/test_mqtt.c
index 36e24adf..32f08e67 100644
--- a/test/unit/mqtt/test_mqtt.c
+++ b/test/unit/mqtt/test_mqtt.c
@@ -47,6 +47,7 @@ mqtt_setup(void)
   old_netif_default = netif_default;
   netif_list = NULL;
   netif_default = NULL;
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void
@@ -57,6 +58,7 @@ mqtt_teardown(void)
   /* restore netif_list for next tests (e.g. loopif) */
   netif_list = old_netif_list;
   netif_default = old_netif_default;
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void test_mqtt_connection_cb(mqtt_client_t *client, void *arg, mqtt_connection_status_t status)
@@ -95,6 +97,10 @@ START_TEST(basic_connect)
   if (client->conn->recv(client->conn->callback_arg, client->conn, p, ERR_OK) != ERR_OK) {
     pbuf_free(p);
   }
+
+  mqtt_disconnect(client);
+  /* fixme: mqtt_client_fre() is missing... */
+  mem_free(client);
 }
 END_TEST
 
diff --git a/test/unit/tcp/test_tcp.c b/test/unit/tcp/test_tcp.c
index 3edde8b6..9db2369b 100644
--- a/test/unit/tcp/test_tcp.c
+++ b/test/unit/tcp/test_tcp.c
@@ -58,6 +58,7 @@ tcp_setup(void)
 
   test_tcp_timer = 0;
   tcp_remove_all();
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void
@@ -69,6 +70,7 @@ tcp_teardown(void)
   /* restore netif_list for next tests (e.g. loopif) */
   netif_list = old_netif_list;
   netif_default = old_netif_default;
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 
diff --git a/test/unit/tcp/test_tcp_oos.c b/test/unit/tcp/test_tcp_oos.c
index 2f87833f..a190e7dc 100644
--- a/test/unit/tcp/test_tcp_oos.c
+++ b/test/unit/tcp/test_tcp_oos.c
@@ -129,6 +129,7 @@ tcp_oos_setup(void)
   netif_list = NULL;
   netif_default = NULL;
   tcp_remove_all();
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void
@@ -140,6 +141,7 @@ tcp_oos_teardown(void)
   /* restore netif_list for next tests (e.g. loopif) */
   netif_list = old_netif_list;
   netif_default = old_netif_default;
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 
diff --git a/test/unit/udp/test_udp.c b/test/unit/udp/test_udp.c
index 147822f4..4ad693e9 100644
--- a/test/unit/udp/test_udp.c
+++ b/test/unit/udp/test_udp.c
@@ -28,12 +28,14 @@ static void
 udp_setup(void)
 {
   udp_remove_all();
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }
 
 static void
 udp_teardown(void)
 {
   udp_remove_all();
+  lwip_check_ensure_no_alloc(SKIP_POOL(MEMP_SYS_TIMEOUT));
 }