From a941422fa6c2997827dd776f8728f788312466a7 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 9 Apr 2026 08:36:40 -1000
Subject: [PATCH] Add unit tests for format_hex helpers

---
 tests/components/core/test_helpers.cpp | 120 +++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 tests/components/core/test_helpers.cpp

diff --git a/tests/components/core/test_helpers.cpp b/tests/components/core/test_helpers.cpp
new file mode 100644
index 0000000000..c6fd070446
--- /dev/null
+++ b/tests/components/core/test_helpers.cpp
@@ -0,0 +1,120 @@
+#include <gtest/gtest.h>
+#include <cstring>
+
+#include "esphome/core/helpers.h"
+
+namespace esphome::testing {
+
+// --- format_hex_to() ---
+
+TEST(FormatHexTo, Basic) {
+  const uint8_t data[] = {0xAB, 0xCD, 0xEF};
+  char buffer[7];  // 3 * 2 + 1
+  format_hex_to(buffer, data, 3);
+  EXPECT_STREQ(buffer, "abcdef");
+}
+
+TEST(FormatHexTo, SingleByte) {
+  const uint8_t data[] = {0x0F};
+  char buffer[3];
+  format_hex_to(buffer, data, 1);
+  EXPECT_STREQ(buffer, "0f");
+}
+
+TEST(FormatHexTo, ZeroLength) {
+  char buffer[4] = "xxx";
+  format_hex_to(buffer, static_cast<size_t>(sizeof(buffer)), static_cast<const uint8_t *>(nullptr), 0);
+  EXPECT_STREQ(buffer, "");
+}
+
+TEST(FormatHexTo, ZeroBufferSize) {
+  char buffer[4] = "xxx";
+  const uint8_t data[] = {0xAB};
+  format_hex_to(buffer, static_cast<size_t>(0), data, 1);
+  // Should not crash, buffer unchanged
+  EXPECT_EQ(buffer[0], 'x');
+}
+
+TEST(FormatHexTo, BufferTooSmall) {
+  const uint8_t data[] = {0xAB, 0xCD, 0xEF};
+  char buffer[5];  // only room for 2 bytes
+  format_hex_to(buffer, data, 3);
+  EXPECT_STREQ(buffer, "abcd");
+}
+
+TEST(FormatHexTo, MacAddress) {
+  const uint8_t mac[] = {0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF};
+  char buffer[13];
+  format_hex_to(buffer, mac, 6);
+  EXPECT_STREQ(buffer, "aabbccddeeff");
+}
+
+// --- format_hex_pretty_to() ---
+
+TEST(FormatHexPrettyTo, BasicColon) {
+  const uint8_t data[] = {0xAB, 0xCD, 0xEF};
+  char buffer[9];  // 3 * 3
+  format_hex_pretty_to(buffer, data, 3);
+  EXPECT_STREQ(buffer, "AB:CD:EF");
+}
+
+TEST(FormatHexPrettyTo, SingleByte) {
+  const uint8_t data[] = {0x0F};
+  char buffer[3];
+  format_hex_pretty_to(buffer, data, 1);
+  EXPECT_STREQ(buffer, "0F");
+}
+
+TEST(FormatHexPrettyTo, ZeroLength) {
+  char buffer[4] = "xxx";
+  format_hex_pretty_to(buffer, static_cast<size_t>(sizeof(buffer)), static_cast<const uint8_t *>(nullptr), 0);
+  EXPECT_STREQ(buffer, "");
+}
+
+TEST(FormatHexPrettyTo, ZeroBufferSize) {
+  char buffer[4] = "xxx";
+  const uint8_t data[] = {0xAB};
+  format_hex_pretty_to(buffer, static_cast<size_t>(0), data, 1);
+  EXPECT_EQ(buffer[0], 'x');
+}
+
+TEST(FormatHexPrettyTo, CustomSeparator) {
+  const uint8_t data[] = {0xAA, 0xBB, 0xCC};
+  char buffer[9];
+  format_hex_pretty_to(buffer, data, 3, ':');
+  EXPECT_STREQ(buffer, "AA:BB:CC");
+}
+
+// --- format_mac_addr_upper() ---
+
+TEST(FormatMacAddrUpper, Basic) {
+  const uint8_t mac[] = {0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF};
+  char buffer[MAC_ADDRESS_PRETTY_BUFFER_SIZE];
+  format_mac_addr_upper(mac, buffer);
+  EXPECT_STREQ(buffer, "AA:BB:CC:DD:EE:FF");
+}
+
+TEST(FormatMacAddrUpper, AllZeros) {
+  const uint8_t mac[] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+  char buffer[MAC_ADDRESS_PRETTY_BUFFER_SIZE];
+  format_mac_addr_upper(mac, buffer);
+  EXPECT_STREQ(buffer, "00:00:00:00:00:00");
+}
+
+// --- format_hex_char() ---
+
+TEST(FormatHexChar, LowercaseDigits) {
+  EXPECT_EQ(format_hex_char(0), '0');
+  EXPECT_EQ(format_hex_char(9), '9');
+  EXPECT_EQ(format_hex_char(10), 'a');
+  EXPECT_EQ(format_hex_char(15), 'f');
+}
+
+TEST(FormatHexChar, UppercaseDigits) {
+  EXPECT_EQ(format_hex_pretty_char(0), '0');
+  EXPECT_EQ(format_hex_pretty_char(9), '9');
+  EXPECT_EQ(format_hex_pretty_char(10), 'A');
+  EXPECT_EQ(format_hex_pretty_char(15), 'F');
+}
+
+}  // namespace esphome::testing