add tests

tests/components/core/test_value_accuracy.cpp

@@ -149,4 +149,73 @@ TEST(ValueAccuracyToBuf, ReturnsCorrectLength) {
   EXPECT_EQ(strlen(buf), len);
 }
 
+// --- value_accuracy_with_uom_to_buf ---
+
+static std::string va_uom_to_string(float value, int8_t accuracy_decimals, const char *uom) {
+  char buf[VALUE_ACCURACY_MAX_LEN];
+  std::span<char, VALUE_ACCURACY_MAX_LEN> sp(buf);
+  StringRef ref(uom);
+  size_t len = value_accuracy_with_uom_to_buf(sp, value, accuracy_decimals, ref);
+  return std::string(buf, len);
+}
+
+static std::string va_uom_reference(float value, int8_t accuracy_decimals, const char *uom) {
+  char buf[VALUE_ACCURACY_MAX_LEN];
+  if (!uom || *uom == '\0') {
+    snprintf(buf, sizeof(buf), "%.*f", accuracy_decimals, value);
+  } else {
+    snprintf(buf, sizeof(buf), "%.*f %s", accuracy_decimals, value, uom);
+  }
+  return std::string(buf);
+}
+
+TEST(ValueAccuracyWithUomToBuf, BasicWithUnit) {
+  EXPECT_EQ(va_uom_to_string(23.456f, 2, "°C"), va_uom_reference(23.456f, 2, "°C"));
+  EXPECT_EQ(va_uom_to_string(1013.25f, 2, "hPa"), va_uom_reference(1013.25f, 2, "hPa"));
+  EXPECT_EQ(va_uom_to_string(-40.0f, 1, "°F"), va_uom_reference(-40.0f, 1, "°F"));
+  EXPECT_EQ(va_uom_to_string(100.0f, 0, "%"), va_uom_reference(100.0f, 0, "%"));
+}
+
+TEST(ValueAccuracyWithUomToBuf, EmptyUnit) {
+  EXPECT_EQ(va_uom_to_string(23.456f, 2, ""), "23.46");
+  EXPECT_EQ(va_uom_to_string(0.0f, 1, ""), "0.0");
+}
+
+TEST(ValueAccuracyWithUomToBuf, ReturnsCorrectLength) {
+  char buf[VALUE_ACCURACY_MAX_LEN];
+  std::span<char, VALUE_ACCURACY_MAX_LEN> sp(buf);
+  StringRef ref("°C");
+  size_t len = value_accuracy_with_uom_to_buf(sp, 23.46f, 2, ref);
+  EXPECT_EQ(strlen(buf), len);
+  EXPECT_EQ(len, strlen("23.46 °C"));
+}
+
+TEST(ValueAccuracyWithUomToBuf, NearBufferLimitTruncates) {
+  // Build a unit long enough that value + " " + unit exceeds VALUE_ACCURACY_MAX_LEN.
+  // "23.46" (5) + " " (1) + unit -> must cap at buf.size()-1 and stay null-terminated.
+  std::string long_unit(VALUE_ACCURACY_MAX_LEN, 'U');
+  char buf[VALUE_ACCURACY_MAX_LEN];
+  std::span<char, VALUE_ACCURACY_MAX_LEN> sp(buf);
+  StringRef ref(long_unit.c_str());
+  size_t len = value_accuracy_with_uom_to_buf(sp, 23.46f, 2, ref);
+  EXPECT_LT(len, VALUE_ACCURACY_MAX_LEN);
+  EXPECT_EQ(strlen(buf), len);
+  // Should begin with the formatted value and a separator.
+  EXPECT_EQ(std::string(buf, 6), "23.46 ");
+}
+
+TEST(ValueAccuracyWithUomToBuf, MatchesSnprintf) {
+  const char *units[] = {"°C", "hPa", "%", "W", "kWh", "m/s"};
+  float values[] = {0.0f, 23.456f, -40.0f, 1013.25f, 100.0f};
+  int8_t accs[] = {0, 1, 2, 3};
+  for (const char *u : units) {
+    for (float v : values) {
+      for (int8_t a : accs) {
+        EXPECT_EQ(va_uom_to_string(v, a, u), va_uom_reference(v, a, u))
+            << "value=" << v << " acc=" << static_cast<int>(a) << " uom=" << u;
+      }
+    }
+  }
+}
+
 }  // namespace esphome::core::testing