[ethernet] Skip setters that pass the default PHY address, MDC, MDIO, clock and SPI interface (#20070)

tests/component_tests/ethernet/config/rmii_custom.yaml

@@ -0,0 +1,14 @@
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+
+ethernet:
+  type: LAN8720
+  mdc_pin: GPIO4
+  mdio_pin: GPIO5
+  phy_addr: 1
+  clk:
+    mode: CLK_OUT
+    pin: GPIO17

tests/component_tests/ethernet/config/rmii_defaults.yaml

@@ -0,0 +1,13 @@
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+
+ethernet:
+  type: LAN8720
+  mdc_pin: GPIO23
+  mdio_pin: GPIO18
+  clk:
+    mode: CLK_EXT_IN
+    pin: GPIO0

tests/component_tests/ethernet/config/spi_s3_own_bus.yaml

@@ -0,0 +1,14 @@
+esphome:
+  name: test
+
+esp32:
+  board: esp32-s3-devkitc-1
+
+ethernet:
+  type: W5500
+  clk_pin: GPIO12
+  mosi_pin: GPIO11
+  miso_pin: GPIO13
+  cs_pin: GPIO10
+  interrupt_pin: GPIO4
+  clock_speed: 20MHz

tests/component_tests/ethernet/test_default_setters.py

@@ -0,0 +1,49 @@
+"""Ethernet setters are skipped when the config matches the C++ initializers."""
+
+from collections.abc import Callable
+from pathlib import Path
+
+_MDIO_SETTERS = ("set_phy_addr(", "set_mdc_pin(", "set_mdio_pin(")
+
+
+def test_rmii_defaults_are_not_emitted(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    main_cpp = generate_main(component_config_path("rmii_defaults.yaml"))
+
+    for setter in (*_MDIO_SETTERS, "set_clk_mode(", "set_clk_pin("):
+        assert setter not in main_cpp
+
+
+def test_rmii_custom_values_are_emitted(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    main_cpp = generate_main(component_config_path("rmii_custom.yaml"))
+
+    assert "set_phy_addr(1);" in main_cpp
+    assert "set_mdc_pin(4);" in main_cpp
+    assert "set_mdio_pin(5);" in main_cpp
+    assert "set_clk_mode(::EMAC_CLK_OUT);" in main_cpp
+    assert "set_clk_pin(17);" in main_cpp
+
+
+def test_spi2_interface_is_not_emitted(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """ESP32-S3 defaults to spi2, which is the C++ initializer."""
+    main_cpp = generate_main(component_config_path("spi_s3_own_bus.yaml"))
+
+    assert "set_interface(" not in main_cpp
+
+
+def test_spi3_interface_is_emitted(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """Classic ESP32 defaults to spi3, so the setter is still needed."""
+    main_cpp = generate_main(component_config_path("spi_own_bus.yaml"))
+
+    assert "set_interface(::SPI3_HOST);" in main_cpp