diff --git a/openbsc/tests/oap/oap_test.c b/openbsc/tests/oap/oap_test.c
index b03c8dc..9a2063b 100644
--- a/openbsc/tests/oap/oap_test.c
+++ b/openbsc/tests/oap/oap_test.c
@@ -27,10 +27,195 @@
 
 #include <stdio.h>
 
-
-static void test_oap(void)
+static void test_oap_api(void)
 {
-	printf("not implemented\n");
+	printf("Testing OAP API\n  - Config parsing\n");
+
+	struct oap_config _config;
+	struct oap_config *config = &_config;
+
+	struct oap_state _state;
+	struct oap_state *state = &_state;
+
+	memset(config, 0, sizeof(*config));
+	memset(state, 0, sizeof(*state));
+
+	OSMO_ASSERT(osmo_hexparse("0102030405060708090a0b0c0d0e0f10", config->secret_k, 16) == 16);
+	OSMO_ASSERT(osmo_hexparse("1112131415161718191a1b1c1d1e1f20", config->secret_opc, 16) == 16);
+
+	/* make sure filling with zeros means uninitialized */
+	OSMO_ASSERT(state->state == OAP_UNINITIALIZED);
+
+	/* invalid client_id and shared secret */
+	config->client_id = 0;
+	config->secret_k_present = 0;
+	config->secret_opc_present = 0;
+	OSMO_ASSERT( oap_init(config, state) == 0 );
+	OSMO_ASSERT(state->state == OAP_DISABLED);
+
+	/* reset state */
+	memset(state, 0, sizeof(*state));
+
+	/* only client_id is invalid */
+	config->client_id = 0;
+	config->secret_k_present = 1;
+	config->secret_opc_present = 1;
+	OSMO_ASSERT( oap_init(config, state) == 0 );
+	OSMO_ASSERT(state->state == OAP_DISABLED);
+
+	memset(state, 0, sizeof(*state));
+
+	/* valid id, but omitted shared_secret (1/2) */
+	config->client_id = 12345;
+	config->secret_k_present = 0;
+	config->secret_opc_present = 1;
+	OSMO_ASSERT( oap_init(config, state) == 0 );
+	OSMO_ASSERT(state->state == OAP_DISABLED);
+
+	memset(state, 0, sizeof(*state));
+
+	/* valid id, but omitted shared_secret (2/2) */
+	config->client_id = 12345;
+	config->secret_k_present = 1;
+	config->secret_opc_present = 0;
+	OSMO_ASSERT( oap_init(config, state) == 0 );
+	OSMO_ASSERT(state->state == OAP_DISABLED);
+
+	memset(state, 0, sizeof(*state));
+
+
+	/* mint configuration */
+	config->client_id = 12345;
+	config->secret_k_present = 1;
+	config->secret_opc_present = 1;
+	/*config->secret_* buffers are still set from the top */
+	OSMO_ASSERT( oap_init(config, state) == 0 );
+	OSMO_ASSERT(state->state == OAP_INITIALIZED);
+
+	printf("  - AUTN failures\n");
+
+	struct oap_message oap_rx;
+	struct oap_message oap_tx;
+	struct msgb *msg_rx;
+	struct msgb *msg_tx;
+
+	memset(&oap_rx, 0, sizeof(oap_rx));
+
+	/* Missing challenge data */
+	oap_rx.message_type = OAP_MSGT_CHALLENGE_REQUEST;
+	oap_rx.rand_present = 0;
+	oap_rx.autn_present = 0;
+	msg_rx = oap_encoded(&oap_rx);
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == -2);
+	msgb_free(msg_rx);
+	OSMO_ASSERT(!msg_tx);
+
+	/* AUTN missing */
+	osmo_hexparse("0102030405060708090a0b0c0d0e0f10",
+		      oap_rx.rand, 16);
+	oap_rx.rand_present = 1;
+	msg_rx = oap_encoded(&oap_rx);
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == -2);
+	msgb_free(msg_rx);
+	OSMO_ASSERT(!msg_tx);
+
+	/* RAND missing */
+	oap_rx.rand_present = 0;
+	osmo_hexparse("cec4e3848a33000086781158ca40f136",
+		      oap_rx.autn, 16);
+	oap_rx.autn_present = 1;
+	msg_rx = oap_encoded(&oap_rx);
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == -2);
+	msgb_free(msg_rx);
+	OSMO_ASSERT(!msg_tx);
+
+	/* wrong autn (by one bit) */
+	osmo_hexparse("0102030405060708090a0b0c0d0e0f10",
+		      oap_rx.rand, 16);
+	osmo_hexparse("dec4e3848a33000086781158ca40f136",
+		      oap_rx.autn, 16);
+	oap_rx.rand_present = 1;
+	oap_rx.autn_present = 1;
+	msg_rx = oap_encoded(&oap_rx);
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == -2);
+	msgb_free(msg_rx);
+	OSMO_ASSERT(!msg_tx);
+
+	/* all data correct */
+	osmo_hexparse("cec4e3848a33000086781158ca40f136",
+		      oap_rx.autn, 16);
+	msg_rx = oap_encoded(&oap_rx);
+
+	/* but refuse to evaluate in uninitialized state */
+	OSMO_ASSERT(state->state == OAP_INITIALIZED);
+
+	state->state = OAP_UNINITIALIZED;
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == -1);
+	OSMO_ASSERT(!msg_tx);
+
+	state->state = OAP_DISABLED;
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == -1);
+	OSMO_ASSERT(!msg_tx);
+
+	state->state = OAP_INITIALIZED;
+
+	/* now everything is correct */
+	printf("  - AUTN success\n");
+	/* a successful return value here indicates correct autn */
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == 0);
+	msgb_free(msg_rx);
+
+	/* Expect the challenge response in msg_tx */
+	OSMO_ASSERT(msg_tx);
+	OSMO_ASSERT(oap_decode(msg_tx->data, msg_tx->len, &oap_tx) == 0);
+	OSMO_ASSERT(oap_tx.message_type == OAP_MSGT_CHALLENGE_RESULT);
+	OSMO_ASSERT(strcmp("e2d05b598c61d9ba",
+			   osmo_hexdump_nospc(oap_tx.xres, sizeof(oap_tx.xres)))
+		    == 0);
+	OSMO_ASSERT(state->state == OAP_SENT_CHALLENGE_RESULT);
+	msgb_free(msg_tx);
+	msg_tx = 0;
+
+	struct oap_state saved_state = _state;
+
+	printf("  - Registration failure\n");
+
+	memset(&oap_rx, 0, sizeof(oap_rx));
+	oap_rx.message_type = OAP_MSGT_REGISTER_ERROR;
+	oap_rx.cause = GMM_CAUSE_PROTO_ERR_UNSPEC;
+	msg_rx = oap_encoded(&oap_rx);
+
+	/* Receive registration error for the first time. */
+	OSMO_ASSERT(state->registration_failures == 0);
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == 0);
+	OSMO_ASSERT(state->registration_failures == 1);
+	OSMO_ASSERT(msg_tx);
+	OSMO_ASSERT(oap_decode(msg_tx->data, msg_tx->len, &oap_tx) == 0);
+	OSMO_ASSERT(oap_tx.message_type == OAP_MSGT_REGISTER_REQUEST);
+	OSMO_ASSERT(state->state == OAP_REQUESTED_CHALLENGE);
+	msgb_free(msg_tx);
+	msg_tx = 0;
+
+	/* Receive registration error for the Nth time. */
+	state->registration_failures = 999;
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == -11);
+	OSMO_ASSERT(!msg_tx);
+	OSMO_ASSERT(state->state == OAP_INITIALIZED);
+	msgb_free(msg_tx);
+	msg_tx = 0;
+
+	msgb_free(msg_rx);
+
+	printf("  - Registration success\n");
+
+	_state = saved_state;
+	memset(&oap_rx, 0, sizeof(oap_rx));
+	oap_rx.message_type = OAP_MSGT_REGISTER_RESULT;
+	msg_rx = oap_encoded(&oap_rx);
+	OSMO_ASSERT(oap_handle(state, msg_rx, &msg_tx) == 0);
+	OSMO_ASSERT(!msg_tx);
+	OSMO_ASSERT(state->state == OAP_REGISTERED);
+	msgb_free(msg_rx);
 }
 
 static struct log_info_cat gprs_categories[] = {
@@ -50,7 +235,7 @@
 {
 	osmo_init_logging(&info);
 
-	test_oap();
+	test_oap_api();
 	printf("Done\n");
 
 	return 0;