[sht4x] Move timestamp update after successful command, add heater test

Only advance last_heater_millis_ after the heater command succeeds
so a failed write retries on the next cycle instead of silently
skipping.

Add heater settings to the test YAML to ensure CI exercises the
heater code path.

esphome/components/sht4x/sht4x.cpp

@@ -86,11 +86,6 @@ void SHT4XComponent::update() {
     uint32_t now = millis();
     if (now - this->last_heater_millis_ >= this->heater_interval_) {
       use_heater = true;
-      // Ensure at least one normal measurement between heater cycles by
-      // pushing the next eligible heater time forward by one update interval.
-      // The configured duty cycle is a maximum, not an exact target.
-      uint32_t interval = std::max(this->heater_interval_, this->get_update_interval());
-      this->last_heater_millis_ = now - this->heater_interval_ + interval;
     }
   }
 
@@ -104,6 +99,12 @@ void SHT4XComponent::update() {
       this->status_set_warning(LOG_STR("Failed to send heater command"));
       return;
     }
+    // Only update timestamp after successful command. Ensure at least one
+    // normal measurement between heater cycles by pushing the next eligible
+    // heater time forward by at least one update interval.
+    uint32_t now = millis();
+    uint32_t interval = std::max(this->heater_interval_, this->get_update_interval());
+    this->last_heater_millis_ = now - this->heater_interval_ + interval;
     return;
   }
 

tests/components/sht4x/common.yaml

@@ -6,4 +6,8 @@ sensor:
     humidity:
       name: SHT4X Humidity
     address: 0x44
+    precision: High
+    heater_max_duty: 0.02
+    heater_power: High
+    heater_time: Long
     update_interval: 15s