diff --git a/arch/sandbox/include/asm/test.h b/arch/sandbox/include/asm/test.h
index 05f66f7..8363ca73 100644
--- a/arch/sandbox/include/asm/test.h
+++ b/arch/sandbox/include/asm/test.h
@@ -58,6 +58,12 @@
 };
 
 /**
+ */
+enum cros_ec_test_t {
+	CROSECT_BREAK_HELLO	= BIT(1),
+};
+
+/**
  * sandbox_i2c_set_test_mode() - set test mode for running unit tests
  *
  * See sandbox_i2c_xfer() for the behaviour changes.
@@ -260,4 +266,12 @@
  */
 void sandbox_set_enable_memio(bool enable);
 
+/**
+ * sandbox_cros_ec_set_test_flags() - Set behaviour for testing purposes
+ *
+ * @dev: Device to check
+ * @flags: Flags to control behaviour (CROSECT_...)
+ */
+void sandbox_cros_ec_set_test_flags(struct udevice *dev, uint flags);
+
 #endif
diff --git a/drivers/misc/cros_ec.c b/drivers/misc/cros_ec.c
index f03b7d5..013c67e 100644
--- a/drivers/misc/cros_ec.c
+++ b/drivers/misc/cros_ec.c
@@ -591,6 +591,25 @@
 	return 0;
 }
 
+int cros_ec_hello(struct udevice *dev, uint *handshakep)
+{
+	struct ec_params_hello req;
+	struct ec_response_hello *resp;
+
+	req.in_data = 0x12345678;
+	if (ec_command_inptr(dev, EC_CMD_HELLO, 0, &req, sizeof(req),
+			     (uint8_t **)&resp, sizeof(*resp)) < 0)
+		return -EIO;
+	if (resp->out_data != req.in_data + 0x01020304) {
+		printf("Received invalid handshake %x\n", resp->out_data);
+		if (handshakep)
+			*handshakep = req.in_data;
+		return -ENOTSYNC;
+	}
+
+	return 0;
+}
+
 int cros_ec_reboot(struct udevice *dev, enum ec_reboot_cmd cmd, uint8_t flags)
 {
 	struct ec_params_reboot_ec p;
@@ -738,7 +757,6 @@
 {
 	struct cros_ec_dev *cdev = dev_get_uclass_priv(dev);
 	struct ec_params_hello req;
-	struct ec_response_hello *resp;
 
 	struct dm_cros_ec_ops *ops;
 	int ret;
@@ -767,14 +785,14 @@
 	/* Try sending a version 3 packet */
 	cdev->protocol_version = 3;
 	req.in_data = 0;
-	if (ec_command_inptr(dev, EC_CMD_HELLO, 0, &req, sizeof(req),
-			     (uint8_t **)&resp, sizeof(*resp)) > 0)
+	ret = cros_ec_hello(dev, NULL);
+	if (!ret || ret == -ENOTSYNC)
 		return 0;
 
 	/* Try sending a version 2 packet */
 	cdev->protocol_version = 2;
-	if (ec_command_inptr(dev, EC_CMD_HELLO, 0, &req, sizeof(req),
-			     (uint8_t **)&resp, sizeof(*resp)) > 0)
+	ret = cros_ec_hello(dev, NULL);
+	if (!ret || ret == -ENOTSYNC)
 		return 0;
 
 	/*
@@ -790,18 +808,16 @@
 
 int cros_ec_test(struct udevice *dev)
 {
-	struct ec_params_hello req;
-	struct ec_response_hello *resp;
+	uint out_data;
+	int ret;
 
-	req.in_data = 0x12345678;
-	if (ec_command_inptr(dev, EC_CMD_HELLO, 0, &req, sizeof(req),
-		       (uint8_t **)&resp, sizeof(*resp)) < sizeof(*resp)) {
+	ret = cros_ec_hello(dev, &out_data);
+	if (ret == -ENOTSYNC) {
+		printf("Received invalid handshake %x\n", out_data);
+		return ret;
+	} else if (ret) {
 		printf("ec_command_inptr() returned error\n");
-		return -1;
-	}
-	if (resp->out_data != req.in_data + 0x01020304) {
-		printf("Received invalid handshake %x\n", resp->out_data);
-		return -1;
+		return ret;
 	}
 
 	return 0;
diff --git a/drivers/misc/cros_ec_sandbox.c b/drivers/misc/cros_ec_sandbox.c
index 9fd6cc2..1922a9c 100644
--- a/drivers/misc/cros_ec_sandbox.c
+++ b/drivers/misc/cros_ec_sandbox.c
@@ -18,6 +18,7 @@
 #include <asm/malloc.h>
 #include <asm/state.h>
 #include <asm/sdl.h>
+#include <asm/test.h>
 #include <linux/input.h>
 
 /*
@@ -73,6 +74,7 @@
  * @matrix: Information about keyboard matrix
  * @keyscan: Current keyscan information (bit set for each row/column pressed)
  * @recovery_req: Keyboard recovery requested
+ * @test_flags: Flags that control behaviour for tests
  */
 struct ec_state {
 	u8 vbnv_context[EC_VBNV_BLOCK_SIZE_V2];
@@ -84,6 +86,7 @@
 	struct ec_keymatrix_entry *matrix;	/* the key matrix info */
 	uint8_t keyscan[KEYBOARD_COLS];
 	bool recovery_req;
+	uint test_flags;
 } s_state, *g_state;
 
 /**
@@ -295,6 +298,8 @@
 		struct ec_response_hello *resp = resp_data;
 
 		resp->out_data = req->in_data + 0x01020304;
+		if (ec->test_flags & CROSECT_BREAK_HELLO)
+			resp->out_data++;
 		len = sizeof(*resp);
 		break;
 	}
@@ -518,6 +523,13 @@
 	}
 }
 
+void sandbox_cros_ec_set_test_flags(struct udevice *dev, uint flags)
+{
+	struct ec_state *ec = dev_get_priv(dev);
+
+	ec->test_flags = flags;
+}
+
 int cros_ec_probe(struct udevice *dev)
 {
 	struct ec_state *ec = dev_get_priv(dev);
diff --git a/include/cros_ec.h b/include/cros_ec.h
index f187bd0..f57e0cc 100644
--- a/include/cros_ec.h
+++ b/include/cros_ec.h
@@ -497,4 +497,15 @@
  */
 int cros_ec_set_lid_shutdown_mask(struct udevice *dev, int enable);
 
+/**
+ * cros_ec_hello() - Send a hello message
+ *
+ * Sends a message with a fixed input value and checks that the expected output
+ * value is received
+ *
+ * @dev: CROS-EC device
+ * @handshakep: If non-NULL, returns received handshake value on error
+ * @return 0 if OK, -ve on error
+ */
+int cros_ec_hello(struct udevice *dev, uint *handshakep);
 #endif
diff --git a/test/dm/Makefile b/test/dm/Makefile
index 46e076e..afcabfa 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -24,6 +24,7 @@
 obj-$(CONFIG_BUTTON) += button.o
 obj-$(CONFIG_DM_BOOTCOUNT) += bootcount.o
 obj-$(CONFIG_CLK) += clk.o clk_ccf.o
+obj-$(CONFIG_CROS_EC) += cros_ec.o
 obj-$(CONFIG_DEVRES) += devres.o
 obj-$(CONFIG_VIDEO_MIPI_DSI) += dsi_host.o
 obj-$(CONFIG_DM_ETH) += eth.o
diff --git a/test/dm/cros_ec.c b/test/dm/cros_ec.c
new file mode 100644
index 0000000..823245c
--- /dev/null
+++ b/test/dm/cros_ec.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright 2021 Google LLC
+ */
+
+#include <common.h>
+#include <cros_ec.h>
+#include <dm.h>
+#include <asm/test.h>
+#include <dm/test.h>
+#include <test/ut.h>
+
+static int dm_test_cros_ec_hello(struct unit_test_state *uts)
+{
+	struct udevice *dev;
+	uint val;
+
+	ut_assertok(uclass_first_device_err(UCLASS_CROS_EC, &dev));
+
+	ut_assertok(cros_ec_hello(dev, NULL));
+
+	val = 0xdead1357;
+	ut_assertok(cros_ec_hello(dev, &val));
+	ut_asserteq(0xdead1357, val);
+
+	sandbox_cros_ec_set_test_flags(dev, CROSECT_BREAK_HELLO);
+	ut_asserteq(-ENOTSYNC, cros_ec_hello(dev, &val));
+	ut_asserteq(0x12345678, val);
+
+	return 0;
+}
+DM_TEST(dm_test_cros_ec_hello, UT_TESTF_SCAN_FDT);