[uart] Share uart_tcp's write pacing and uart_id matcher (#20464)

tests/unit_tests/components/test_uart.py

@@ -0,0 +1,24 @@
+"""Tests for the uart helpers shared by components that own a UART."""
+
+from esphome.components.uart import subtree_references_uart
+from esphome.core import ID
+
+
+def test_finds_a_nested_uart_id() -> None:
+    config = {"modbus": [{"id": ID("hub"), "uart_id": ID("bus")}]}
+    assert subtree_references_uart(config, "bus")
+
+
+def test_ignores_other_uarts_and_other_keys() -> None:
+    config = {"modbus": [{"uart_id": ID("other")}], "sensor": [{"id": ID("bus")}]}
+    assert not subtree_references_uart(config, "bus")
+
+
+def test_finds_another_key() -> None:
+    config = {"modbus_tcp_uart": [{"tcp_uart_id": ID("bus")}]}
+    assert subtree_references_uart(config, "bus", "tcp_uart_id")
+    assert not subtree_references_uart(config, "bus")
+
+
+def test_handles_scalars() -> None:
+    assert not subtree_references_uart("bus", "bus")