diff --git a/tests/test_i2c.c b/tests/test_i2c.c
new file mode 100644
index 0000000..067d551
--- /dev/null
+++ b/tests/test_i2c.c
@@ -0,0 +1,263 @@
+/* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */
+
+#if HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "compiler.h"
+#include "range.h"
+#include "libmctp-log.h"
+#include "libmctp-i2c.h"
+#include "libmctp-sizes.h"
+#include "libmctp-alloc.h"
+
+/* For access to mctp_bninding_i2c internals */
+#include "i2c-internal.h"
+
+#ifdef NDEBUG
+#undef NDEBUG
+#endif
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+struct mctp_binding_serial_pipe {
+	int ingress;
+	int egress;
+
+	struct mctp_binding_serial *serial;
+};
+
+// Sized to test fragmentation and >8 bit length
+#define TEST_MSG_LEN 300
+static uint8_t mctp_msg_src[TEST_MSG_LEN];
+
+struct i2c_test {
+	struct mctp_binding_i2c *i2c;
+	struct mctp *mctp;
+
+	uint8_t rx_msg[TEST_MSG_LEN];
+	size_t rx_len;
+
+	/* Physical addresses. These get set regardless of whether the packet
+	 * is dropped by the stack (no match etc) */
+	uint8_t last_rx_i2c_src;
+	uint8_t last_tx_i2c_dst;
+};
+
+static const uint8_t I2C_ADDR_A = 0x20;
+static const uint8_t I2C_ADDR_B = 0x21;
+static const uint8_t EID_A = 50;
+static const uint8_t EID_B = 51;
+
+static int test_i2c_tx(const void *buf, size_t len, void *ctx)
+{
+	struct i2c_test *test_pair = ctx;
+	struct i2c_test *tx_test = &test_pair[0];
+	struct i2c_test *rx_test = &test_pair[1];
+
+	mctp_prdebug("test_i2c_tx len %zu", len);
+
+	const struct mctp_i2c_hdr *hdr = buf;
+	tx_test->last_tx_i2c_dst = hdr->dest >> 1;
+	rx_test->last_rx_i2c_src = hdr->source >> 1;
+
+	mctp_i2c_rx(rx_test->i2c, buf, len);
+	return 0;
+}
+
+static void test_i2c_rxmsg(uint8_t src_eid, bool tag_owner, uint8_t msg_tag,
+			   void *ctx, void *msg, size_t len)
+{
+	struct i2c_test *test_pair = ctx;
+	// struct i2c_test *tx_test = &test_pair[0];
+	struct i2c_test *rx_test = &test_pair[1];
+
+	mctp_prdebug("test_i2c_rx src %d len %zu tag %d owner %d", src_eid, len,
+		     msg_tag, tag_owner);
+
+	// Must be cleared by previous test runs
+	assert(rx_test->rx_len == 0);
+	memcpy(rx_test->rx_msg, msg, len);
+	rx_test->rx_len = len;
+}
+
+/* Transmits a MCTP message and checks the received message matches */
+static void run_tx_test(struct i2c_test *tx_test, uint8_t dest_eid,
+			size_t tx_len, struct i2c_test *rx_test)
+{
+	int rc;
+	const uint8_t msg_tag = 2;
+	const bool tag_owner = false;
+
+	assert(tx_len <= sizeof(mctp_msg_src));
+	rc = mctp_message_tx(tx_test->mctp, dest_eid, tag_owner, msg_tag,
+			     mctp_msg_src, tx_len);
+	assert(rc == 0);
+
+	while (!mctp_is_tx_ready(tx_test->mctp, dest_eid)) {
+		mctp_i2c_tx_poll(tx_test->i2c);
+	}
+
+	assert(rx_test->rx_len == tx_len);
+	assert(memcmp(rx_test->rx_msg, mctp_msg_src, tx_len) == 0);
+
+	rx_test->rx_len = 0;
+}
+
+static void test_neigh_expiry(struct i2c_test *tx_test,
+			      struct i2c_test *rx_test)
+{
+	const uint8_t msg_tag = 2;
+	const bool tag_owner = true;
+	const size_t msg_len = 5;
+	int rc;
+
+	(void)rx_test;
+
+	/* Clear the tx neighbour table */
+	memset(tx_test->i2c->neigh, 0x0, sizeof(tx_test->i2c->neigh));
+
+	/* Check that all EIDs fail */
+	rx_test->rx_len = 0;
+	for (size_t eid = 8; eid < 254; eid++) {
+		mctp_message_tx(tx_test->mctp, eid, tag_owner, msg_tag,
+				mctp_msg_src, msg_len);
+		/* Not received */
+		assert(rx_test->rx_len == 0);
+	}
+
+	/* Add one entry */
+	rc = mctp_i2c_set_neighbour(tx_test->i2c, EID_B,
+				    rx_test->i2c->own_addr);
+	assert(rc == 0);
+	rx_test->rx_len = 0;
+	mctp_message_tx(tx_test->mctp, EID_B, tag_owner, msg_tag, mctp_msg_src,
+			msg_len);
+	assert(rx_test->rx_len == msg_len);
+	assert(tx_test->last_tx_i2c_dst == rx_test->i2c->own_addr);
+
+	/* Replace the entry */
+	rx_test->i2c->own_addr++;
+	rc = mctp_i2c_set_neighbour(tx_test->i2c, EID_B,
+				    rx_test->i2c->own_addr);
+	assert(rc == 0);
+	rx_test->rx_len = 0;
+	mctp_message_tx(tx_test->mctp, EID_B, tag_owner, msg_tag, mctp_msg_src,
+			msg_len);
+	assert(rc == 0);
+	assert(rx_test->rx_len == msg_len);
+	assert(tx_test->last_tx_i2c_dst == rx_test->i2c->own_addr);
+
+	/* Check only one entry is set */
+	size_t count = 0;
+	for (size_t i = 0; i < MCTP_I2C_NEIGH_COUNT; i++) {
+		struct mctp_i2c_neigh *n = &tx_test->i2c->neigh[i];
+		if (n->used) {
+			assert(n->eid == EID_B);
+			count++;
+		}
+	}
+	assert(count == 1);
+
+	/* Ensure we can iterate without overflow.
+	 * If MCTP_I2C_NEIGH_COUNT increases too large this test would need rethinking
+	 * (and eviction may become impossible) */
+	assert((int)EID_B + MCTP_I2C_NEIGH_COUNT < 254);
+	assert((int)I2C_ADDR_B + MCTP_I2C_NEIGH_COUNT < 0x7f);
+
+	/* Fill entries. -1 because one was already filled. */
+	for (size_t i = 0; i < MCTP_I2C_NEIGH_COUNT - 1; i++) {
+		/* Unused addresses */
+		uint8_t addr = rx_test->i2c->own_addr + i + 1;
+		uint8_t eid = EID_B + i + 1;
+		rc = mctp_i2c_set_neighbour(tx_test->i2c, eid, addr);
+		assert(rc == 0);
+	}
+
+	/* Check all are used */
+	for (size_t i = 0; i < MCTP_I2C_NEIGH_COUNT; i++) {
+		struct mctp_i2c_neigh *n = &tx_test->i2c->neigh[i];
+		assert(n->used);
+	}
+
+	/* Test eviction */
+	{
+		uint8_t addr =
+			rx_test->i2c->own_addr + MCTP_I2C_NEIGH_COUNT + 1;
+		uint8_t eid = EID_B + MCTP_I2C_NEIGH_COUNT + 1;
+		rc = mctp_i2c_set_neighbour(tx_test->i2c, eid, addr);
+		assert(rc == 0);
+
+		/* EID_B got evicted, send should fail */
+		rx_test->rx_len = 0;
+		mctp_message_tx(tx_test->mctp, EID_B, tag_owner, msg_tag,
+				mctp_msg_src, msg_len);
+		/* Not received */
+		assert(rx_test->rx_len == 0);
+	}
+
+	/* Add EID_B again */
+	rc = mctp_i2c_set_neighbour(tx_test->i2c, EID_B,
+				    rx_test->i2c->own_addr);
+	assert(rc == 0);
+	rx_test->rx_len = 0;
+	mctp_message_tx(tx_test->mctp, EID_B, tag_owner, msg_tag, mctp_msg_src,
+			msg_len);
+	/* Is received */
+	assert(rx_test->rx_len == msg_len);
+}
+
+int main(void)
+{
+	struct i2c_test scenario[2];
+	struct i2c_test *tx_test = &scenario[0];
+	struct i2c_test *rx_test = &scenario[1];
+
+	mctp_set_log_stdio(MCTP_LOG_DEBUG);
+
+	memset(scenario, 0x0, sizeof(scenario));
+
+	/* Setup a source buffer */
+	for (size_t i = 0; i < sizeof(mctp_msg_src); i++) {
+		mctp_msg_src[i] = i & 0xff;
+	}
+
+	tx_test->mctp = mctp_init();
+	assert(tx_test->mctp);
+	tx_test->i2c = malloc(MCTP_SIZEOF_BINDING_I2C);
+	assert(tx_test->i2c);
+	rx_test->mctp = mctp_init();
+	assert(rx_test->mctp);
+	rx_test->i2c = malloc(MCTP_SIZEOF_BINDING_I2C);
+	assert(rx_test->i2c);
+
+	/* TX side */
+	mctp_i2c_setup(tx_test->i2c, I2C_ADDR_A, test_i2c_tx, scenario);
+	mctp_register_bus(tx_test->mctp, mctp_binding_i2c_core(tx_test->i2c),
+			  EID_A);
+	mctp_set_rx_all(tx_test->mctp, NULL, NULL);
+	mctp_i2c_set_neighbour(tx_test->i2c, EID_B, I2C_ADDR_B);
+
+	/* RX side */
+	mctp_i2c_setup(rx_test->i2c, I2C_ADDR_B, NULL, NULL);
+	mctp_register_bus(rx_test->mctp, mctp_binding_i2c_core(rx_test->i2c),
+			  EID_B);
+	mctp_set_rx_all(rx_test->mctp, test_i2c_rxmsg, scenario);
+	// mctp_i2c_set_neighbour(rx_test->i2c, EID_A, I2C_ADDR_A);
+
+	/* Try all message sizes */
+	for (size_t i = 1; i < sizeof(mctp_msg_src); i++) {
+		run_tx_test(tx_test, EID_B, i, rx_test);
+	}
+
+	test_neigh_expiry(tx_test, rx_test);
+
+	return 0;
+}