[power_supply] Make enable_on_boot high priority (#16914)

tests/components/power_supply/test_setup_priority.cpp

@@ -0,0 +1,47 @@
+#include <gtest/gtest.h>
+
+#include "esphome/components/power_supply/power_supply.h"
+#include "esphome/core/gpio.h"
+#include "esphome/core/component.h"
+
+namespace esphome::power_supply::testing {
+
+// Minimal dummy internal GPIO pin implementation for testing
+class DummyInternalPin : public InternalGPIOPin {
+ public:
+  DummyInternalPin() = default;
+  void setup() override {}
+  void pin_mode(esphome::gpio::Flags) override {}
+  esphome::gpio::Flags get_flags() const override { return esphome::gpio::FLAG_NONE; }
+  bool digital_read() override { return false; }
+  void digital_write(bool) override {}
+  void detach_interrupt() const override {}
+  ISRInternalGPIOPin to_isr() const override { return ISRInternalGPIOPin(); }
+  uint8_t get_pin() const override { return 0; }
+  bool is_inverted() const override { return false; }
+
+ protected:
+  // Implement protected attach_interrupt required by InternalGPIOPin
+  void attach_interrupt(void (*func)(void *), void *arg, esphome::gpio::InterruptType type) const override {}
+};
+
+TEST(PowerSupply, HasHigherPriorityThanBusWhenInternalAndEnableOnBoot) {
+  power_supply::PowerSupply ps;
+  DummyInternalPin pin;
+  ps.set_pin(&pin);
+  ps.set_enable_on_boot(true);
+
+  // POWER priority should be greater than BUS priority
+  EXPECT_GT(ps.get_setup_priority(), setup_priority::BUS);
+}
+
+TEST(PowerSupply, FallsBackToIOWhenNotEnableOnBoot) {
+  power_supply::PowerSupply ps;
+  DummyInternalPin pin;
+  ps.set_pin(&pin);
+  ps.set_enable_on_boot(false);
+
+  EXPECT_EQ(ps.get_setup_priority(), setup_priority::IO);
+}
+
+}  // namespace esphome::power_supply::testing